Use of factor-analyzed symptom dimensions to predict outcome with serotonin reuptake inhibitors and placebo in the treatment of obsessive-compulsive disorder.

OBJECTIVE: No consistent predictors of outcome have been identified for the pharmaco-therapy of obsessive-compulsive disorder (OCD). Recent factor analytic studies have identified meaningful symptom dimensions that may be related to response to serotonin reuptake inhibitors and other treatments. METHOD: A total of 354 outpatients with primary OCD were administered the Yale-Brown Obsessive Compulsive Scale Symptom Checklist, and its 13 main symptom categories were factor analyzed by using principal components analysis. The identified symptom dimensions were then entered into multiple regression models as outcome predictors of response to serotonin reuptake inhibitors and placebo response in a group of 150 nondepressed subjects who completed six double-blind, placebo-controlled trials with a serotonin reuptake inhibitor (clomipramine, fluvoxamine, fluoxetine, sertraline, and paroxetine). Eighty-four patients received a serotonin reuptake inhibitor and 66, placebo. RESULTS: The principal components analysis identified five factors that explained 65.5% of variance in outcome: symmetry/ordering, hoarding, contamination/cleaning, aggressive/checking, and sexual/religious obsessions. Serotonin reuptake inhibitors were significantly superior to placebo on all outcome measures. Initial severity of OCD was related to greater posttreatment severity of OCD. Higher scores on the hoarding dimension predicted poorer outcome following treatment with serotonin reuptake inhibitors, after control for baseline severity. No predictors of placebo response were identified. Exclusion of clomipramine did not modify the overall results, suggesting a cross-serotonin reuptake inhibitor effect. CONCLUSIONS: The identified symptom dimensions are largely congruent with those identified in earlier reports. Patients with OCD vary in their response to treatment with serotonin reuptake inhibitors. The presence of hoarding obsessions and compulsions is associated with poorer response to serotonin reuptake inhibitors.     

Neuroendocrine and behavioral responses to challenge with the indirect serotonin agonist dl-fenfluramine in adults with obsessive-compulsive disorder.

Neuroendocrine and behavioral responses to a single 60-mg oral dose of the indirect serotonin agonist dl-fenfluramine were assessed in unmedicated adults with obsessive-compulsive disorder (OCD) and neuroendocrine results contrasted with those in normal control subjects. Net fenfluramine-induced prolactin release did not differ significantly between OCD patients and normal controls. Prolactin responses in the OCD group were not significantly correlated with baseline Yale-Brown Obsessive Compulsive Scale scores for either obsessions or compulsions, but were positively correlated with the baseline Hamilton Depression Scale score and Hamilton Anxiety Scale score. No clear difference in the severity of patients' obsessions or compulsions was found following challenge with fenfluramine versus placebo. Although the present study does not demonstrate a serotonergic abnormality in OCD, this may be more a reflection of limitations of the test procedures than evidence that central nervous system (CNS) serotonergic function is normal in the disorder.     

Long-term follow-up and predictors of clinical outcome in obsessive-compulsive patients treated with serotonin reuptake inhibitors and behavioral therapy

BACKGROUND: The objective of this study was to examine the long-term course of obsessive-compulsive disorder (OCD) in patients treated with serotonin reuptake inhibitors (SRIs) and behavioral therapy and to identify predictors of clinical outcome. METHOD: Sixty outpatients meeting DSM-II-R or DSM-IV criteria for OCD were followed up for 1 to 5 years (mean = 2.5 years). All of them received prolonged pharmacologic therapy with an SRI. RESULTS: Thirty-seven patients (61.7%) completed an adequate behavioral treatment. At long-term assessment, 22 patients (36.7%) exhibited a global Yale-Brown Obsessive Compulsive Scale (Y-BOCS) score greater than 16 or a final reduction in Y-BOCS global score of less than 35% and were considered nonresponders. Patients who completed behavioral therapy showed a significant decrease in Y-BOCS compulsions subscale score (p = .01), whereas no significant differences in either Y-BOCS global or obsessions subscale scores between those who did and those who did not undergo behavioral therapy were detected. Obsessions of sexual/religious content were the unique factor related to a poorer long-term outcome. CONCLUSION: A substantial number of OCD patients showed persistent disabling symptoms at the long-term follow-up in spite of combined pharmacologic and behavioral treatment. Major benefits from behavioral therapy appeared to be the improvement of ritualistic behaviors. Sexual/religious obsessions predicted poorer long-term outcome, whereas short-term response to SRI treatment failed to achieve predictive value in the long-term course of OCD.     

Quality of life in obsessive-compulsive disorder: the different impact of obsessions and compulsions

BACKGROUND: Patients with obsessive-compulsive disorder (OCD) are troubled by repeated obsessions and/or compulsions, which seem senseless and frequently repugnant. OBJECTIVE: The study examines the differential impact of obsessions and compulsions on the quality of life (QoL) of patients with OCD. METHODS: Seventy-five patients (43 females, 32 males) between 21 and 62 years old with OCD (ICD 10 F42.0-F42.2) were recruited from the outpatient clinic for anxiety disorders at the Department of Psychiatry of the University of Leipzig. The severity of OCD symptoms was assessed by the Yale Brown Obsessive-Compulsive Scale (a standardized, clinician-administered scale), and depressiveness was assessed with the Beck Depression Inventory (a self-report instrument). QoL was assessed by means of the WHOQOL-BREF, a self-administered questionnaire developed by WHO. RESULTS: Compulsions reduced patients' QoL in the WHOQOL-BREF domains 'physical well-being', 'psychological well-being' and 'environment', whereas obsessions did not have any impact on QoL ratings. Depressive symptoms were a strong predictor of poor QoL in OCD patients. CONCLUSIONS: In order to judge the QoL of OCD patients, obsessions and compulsions have to be considered differently. Diagnosing and treating depressive symptoms is important for improving the QoL in OCD.     

Motivation to change as a predictor of treatment response in obsessive compulsive disorder.

BACKGROUND: Motivation to change has been shown to predict treatment outcome in various areas of mental health but has never been examined in obsessive compulsive disorder (OCD). The purpose of this report is to present the first use of the University of Rhode Island Change Assessment (URICA) in an OCD pharmacotherapy sample and to determine whether motivation to change predicts degree of treatment response in this group. METHODS: The sample consisted of 32 outpatients diagnosed with OCD who completed an open-label 10-week trial of fluvoxamine. Participants completed the URICA at baseline. OCD symptom severity was rated at baseline and end of treatment. RESULTS: While overall readiness was not related to change in severity, high scores on the Precontemplation subscale (indicating greater resistance to changing OC behaviors) were associated with less change pre- to post-treatment. CONCLUSIONS: Preliminary findings indicate that greater resistance to change is associated with less improvement in OCD symptom severity following pharmacotherapy. As this is the first use of the URICA as a predictor of OCD response, future research should further examine the role of motivation to change in treatment outcome in a larger OCD sample.     

Piloting the perinatal obsessive-compulsive scale (POCS): development and validation

Onset/worsening of obsessive-compulsive disorder (OCD) during the perinatal period are frequently seen clinically. No specific tool assessing the unique content, context, severity, and onset of perinatal OCD exists. A self-report scale of perinatal obsessions and compulsions, the Perinatal Obsessive-Compulsive Scale (POCS), was developed and validated. A total of 162 women (67 pregnant, 95 postpartum) participated in this pilot study. They completed the POCS as well as the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS). The POCS has good construct validity, reflected by representative items, high internal consistency, good concurrent validity and discriminative capacity. The most common obsessions were fear of having an unhealthy baby at birth, contamination, the baby being taken away, and infant death. Behavioral compulsions such as repeating rituals, asking for reassurance, checking, and cleaning mirrored these obsessions. The POCS helps clinicians detect perinatal OCD while giving perinatal women an opportunity to openly discuss socially sensitive issues.     

Health concerns in patients with obsessive-compulsive disorder

In the present study, individuals with obsessive-compulsive disorder (OCD) who also had excessive health concerns (n = 56) were compared with OCD individuals without such concerns (n = 343) regarding their OCD symptom severity, types of obsessions and compulsions, insight into the irrationality of their obsessions, and prevalence of generalized anxiety disorder. While the presence of health concerns did not affect the severity of OCD symptoms, the groups differed with respect to the types of symptoms displayed: those with health concerns had more somatic and harm obsessions, and checking compulsions: whereas those without such concerns had more contamination obsessions and washing compulsions. The insight of both groups ranged from poor to excellent, yet the number of individuals with poor insight was greater among those with health concerns than those without. Generalized anxiety disorder was also more prevalent among OCD individuals with excessive health concerns.     

Cognitive dysfunctions in patients with obsessive-compulsive disorder compared to the patients with schizophrenia patients: relation to overvalued ideas

OBJECTIVE: The clinical overlaps between schizophrenia and obsessive-compulsive disorder (OCD) seem to be related to thought disorders involving obsessions, overvalued ideas, and delusions. Overvalued ideas are beliefs falling in between obsessions and delusions and are stronger than obsessions but weaker than delusions. The goal of the present study was to compare patients with OCD to those with schizophrenia in terms of cognitive functions and to relate cognition and overvalued ideas in OCD. METHODS: Twenty three patients with OCD (free of depression), 24 patients with schizophrenia, and 22 healthy subjects matched to patients in age, gender, education, and hand dominance were included in the study. All subjects were administered neurocognitive tests assessing verbal learning-memory, executive functions, verbal fluency, attention and verbal working memory. RESULTS: Patients with schizophrenia showed worse performance on cognitive tests than the OCD and control groups. The severity of overvalued ideas was significantly correlated to cognitive functions in the OCD group. There were no significant differences in cognitive functions between schizophrenia group and the OCD patients who had higher scores on the Overvalued Ideas Scale (OVIS). CONCLUSION: Overvalued ideas in OCD may be related to cognitive dysfunctions in OCD and this subtype of OCD may have similar characteristics to schizophrenia in terms of cognition.     

Initial data on a 5-item measure of OCD symptom severity and change: The obsessive compulsive session change index (OCSCI)

Repeated measurement of symptoms throughout treatment allows providers to assess individual patterns of symptom change. However, outside of a clinical trial, administration of lengthy measures at each session is unlikely. Therefore, in order to bridge the gap between clinical research and actual clinical practice we developed a brief self-report measure of obsessive compulsive symptoms that can be used at each session, the Obsessive Compulsive Session Change Index (OCSCI). The OCSCI assesses time spent on obsessions, time spent on compulsions, interference and distress related to obsessions and compulsions, and relative change in symptoms from the beginning of treatment. This paper reports initial psychometric properties of the OCSCI. Twenty-seven adults receiving exposure and ritual prevention for obsessive compulsive disorder (OCD) completed the OCSCI at each session. Results showed that the OCSCI had good internal consistency, and convergent and divergent validity. Specifically, the OCSCI had moderate to strong correlations with both self-reported and clinician rated OCD. Finally, the OCSCI was not as strongly correlated with depressive symptoms as it was with OCD symptoms. The findings presented herein suggest that the OCSCI can be useful as a measure of client progress throughout treatment.     

Quality of life in OCD: differential impact of obsessions, compulsions, and depression comorbidity.

OBJECTIVE: An anxiety disorder severely affects the sufferer's quality of life (QOL), and this may be particularly true of those with obsessive-compulsive disorder (OCD). This study examines the differential impact of obsessions, compulsions, and depression comorbidity on the QOL of individuals with OCD. METHOD: Forty-three individuals diagnosed with OCD according to DSM-IV criteria and experiencing clinically significant obsessions and compulsions completed measures of QOL, obsessive-compulsive symptom severity, and depression severity. RESULTS: Obsession severity was found to significantly predict patient QOL, whereas the severity of compulsive rituals did not impact on QOL ratings. Comorbid depression severity was the single greatest predictor of poor QOL, accounting for 54% of the variance. CONCLUSIONS: Given the importance of these symptoms, treatments that directly target obsessions and secondary depression symptoms in OCD are warranted. However, replication of these findings in a prospective cohort study is required, because although the the current study's cross-sectional design allows for the examination of the associations among obsessions, depression, and QOL, it cannot establish their temporal framework (that is, causal relations).     

Preschool children with obsessive–compulsive disorder and fluoxetine treatment

Obsessive–compulsive disorder (OCD) is an anxiety disorder which can substantially disable children’s ability to function at home and school. Clinicians frequently rely on knowledge about symptoms that can be examined early in treatment to determine future treatment effectiveness. However, OCD in preschoolers has also received little attention in literature. To the best of our knowledge, there is only one retrospective chart review and one case report in the literature for preschool cases treated with SSRIs. Therefore, the effect of fluoxetine on preschool children was imprecisely understood. The aim of this case report was to examine the efficacy and safety of fluoxetine treatment for pediatric OCD. Four preschool children with OCD completed an 8-week fluoxetine (up to 20 mg) trial. We diagnosed OCD according to Diagnostic and statistical manual of mental disorders, 4th edition, text revision (DSM-IV-TR) criteria and symptoms of OCD were assessed with the Childrens’ Yale-Brown Obsessive Compulsive Scale (CY-BOCS). Initial and post-treatment symptom severity and improvement were assessed by using the severity (S) and improvement (I) scales of Clinical Global Impressions Scale (CGI). The CY-BOCS total, obsessions and compulsions subscale scores and CGI-S scores were significantly improved for all of the cases at the end of the eighth week. In this case report four preschool children, with severe OCD and resistant to the previous non-psychopharmacologic treatment responded well to fluoxetine monotherapy. On the other hand, the usage of SSRIs in preschool children remains highly controversial, due to the lack of data on safety and efficacy.     

OCD symptoms in a sample of Turkish patients: a phenomenological picture

This study aimed to investigate the clinical features of obsessive-compulsive disorder (OCD) and the possible association between obsessive-compulsive symptoms and culture-related characteristics in a sample of Turkish patients with OCD. We studied 141 patients with OCD (according to DSM-IV criteria) consecutively admitted to our outpatient clinic during the period from February 1998 to December 2003. We used the Turkish version of the Structured Clinical Interview for DSM-IV (SCID) to interview all patients, and the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) to assess obsessive-compulsive symptoms and severity. The onset of OCD symptoms was earlier in males. Major depression was the most common comorbid disorder (30.5%). The most commonly occurring obsessions were contamination (56.7%), aggression (48.9%), and somatic (24.1%), followed by religious (19.9%), symmetry (18.4%), and sexual imagery (15.6%). Symmetry and sexual obsessions, and checking compulsions and rituals, tended to be more common in male patients. Dirt and contamination obsessions and washing compulsions were slightly more common in females. The vast majority of patients with religious obsessions (83%) and half of the patients with sexual obsessions had compulsions that included religious practices. Also, patients with sexual and religious obsessions had delayed seeking professional help.     

The Yale-Brown Obsessive Compulsive Scale: factor analysis, construct validity, and suggestions for refinement

The Yale-Brown Obsessive Compulsive Scale (Y-BOCS) is widely acknowledged as the gold standard measure of obsessive-compulsive disorder (OCD) symptom severity. Despite its popularity, a number of questions remain regarding the Y-BOCS' psychometric properties including: (a) whether obsessional and compulsive symptoms contribute independently to global OCD severity and (b) whether the Y-BOCS subscales are valid with respect to other measures of OCD. We examined these issues in a sample of 100 patients with a diagnosis of OCD. While our confirmatory factor analyses failed to reproduce any previously reported models of the Y-BOCS factor structure, exploratory factor analysis indicated a two-factor solution that assessed symptom severity (i.e., time, distress, and interference from obsessions and compulsions) as separate from resistance and control of obsessions and compulsions. In contrast to the Resistance/Control Subscale, the Severity Subscale demonstrated good psychometric properties and construct validity. Based on our findings we recommend revisions to scoring the Y-BOCS.     

The epidemiology of obsessive-compulsive disorder in the National Comorbidity Survey Replication

Despite significant advances in the study of obsessive-compulsive disorder (OCD), important questions remain about the disorder's public health significance, appropriate diagnostic classification, and clinical heterogeneity. These issues were explored using data from the National Comorbidity Survey Replication, a nationally representative survey of US adults. A subsample of 2073 respondents was assessed for lifetime Diagnostic and Statistical Manual of Mental Disorders, 4th edn (DSM-IV) OCD. More than one quarter of respondents reported experiencing obsessions or compulsions at some time in their lives. While conditional probability of OCD was strongly associated with the number of obsessions and compulsions reported, only small proportions of respondents met full DSM-IV criteria for lifetime (2.3%) or 12-month (1.2%) OCD. OCD is associated with substantial comorbidity, not only with anxiety and mood disorders but also with impulse-control and substance use disorders. Severity of OCD, assessed by an adapted version of the Yale-Brown Obsessive Compulsive Scale, is associated with poor insight, high comorbidity, high role impairment, and high probability of seeking treatment. The high prevalence of subthreshold OCD symptoms may help explain past inconsistencies in prevalence estimates across surveys and suggests that the public health burden of OCD may be greater than its low prevalence implies. Evidence of a preponderance of early onset cases in men, high comorbidity with a wide range of disorders, and reliable associations between disorder severity and key outcomes may have implications for how OCD is classified in DSM-V.     

Clinical picture of obsessive-compulsive disorder with poor insight: a regression model

DSM-IV included a type of obsessive-compulsive disorder (OCD) with poor insight in the official classification. The present study was performed using a continuous measure of the level of insight to analyze the association between this variable and characteristics of the disorder. Seventy-four consecutive OCD outpatients (DSM-IV criteria) were assessed using: a semistructured interview for sociodemographic and clinical features, the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS), the National Institute of Mental Health Obsessive-Compulsive Scale (NIMH-OCS), the Hamilton Depression and Anxiety Rating Scales (HDRS, HARS), and the Overvalued Ideas Scale (OVIS) as a continuous measure of the level of insight. Stepwise multiple regression analysis revealed that demographic and clinical factors were related to the OVIS score. The following four factors were found to be significantly related to the OVIS score: the Y-BOCS score for compulsions, OCD chronic course, and family history of OCD were positively related, while obsessive-compulsive personality disorder was negatively related. These results suggest that poor insight identifies a group of OCD patients with distinct clinical characteristics.     

Religiosity and religious obsessions in obsessive-compulsive disorder.

Religion has often been thought to play a part in the genesis of some cases of obsessive-compulsive disorder (OCD). In this study, we explored the relationship between religiosity, religious obsessions, and other clinical characteristics of OCD. Forty-five outpatients with OCD were evaluated with the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) and the Yale-Brown Obsessive-Compulsive Checklist (Y-BOCC) as well as the Religious Practices Index (RPI), which was developed for this study. On the basis of these evaluations, 42% of the patients were found to have religious obsessions. Despite differences in the frequency of religious obsessions found in this study compared with others, a factor analysis revealed the symptom dimensions to be similar to those found in other OCD samples. There was no significant difference in the overall severity of obsessions and compulsions between patients with and without religious obsessions. RPI scores did not differ significantly between groups. We failed to find a relationship between RPI scores or religious obsessions and any particular type of obsession or compulsion. A logistic regression analysis revealed that the sole predictor of the presence of religious obsessions was a higher number of types of obsessions. In conclusion, we failed to find a conclusive relationship between religiosity and any other clinical feature of OCD, including the presence of religious obsessions. On the other hand, we showed that the patients who tend to have a variety of obsessions are more likely also to have religious obsessions. Thus, religion appears to be one more arena where OCD expresses itself, rather than being a determinant of the disorder.     

Phenomenology of OCD: Lessons from a large multicenter study and implications for ICD-11

This study aimed to investigate the phenomenology of obsessive–compulsive disorder (OCD), addressing specific questions about the nature of obsessions and compulsions, and to contribute to the World Health Organization's (WHO) revision of OCD diagnostic guidelines. Data from 1001 patients from the Brazilian Research Consortium on Obsessive–Compulsive Spectrum Disorders were used. Patients were evaluated by trained clinicians using validated instruments, including the Dimensional Yale–Brown Obsessive–Compulsive Scale, the University of Sao Paulo Sensory Phenomena Scale, and the Brown Assessment of Beliefs Scale. The aims were to compare the types of sensory phenomena (SP, subjective experiences that precede or accompany compulsions) in OCD patients with and without tic disorders and to determine the frequency of mental compulsions, the co-occurrence of obsessions and compulsions, and the range of insight. SP were common in the whole sample, but patients with tic disorders were more likely to have physical sensations and urges only. Mental compulsions occurred in the majority of OCD patients. It was extremely rare for OCD patients to have obsessions without compulsions. A wide range of insight into OCD beliefs was observed, with a small subset presenting no insight. The data generated from this large sample will help practicing clinicians appreciate the full range of OCD symptoms and confirm prior studies in smaller samples the degree to which insight varies. These findings also support specific revisions to the WHO's diagnostic guidelines for OCD, such as describing sensory phenomena, mental compulsions and level of insight, so that the world-wide recognition of this disabling disorder is increased.     

Impact of depressive and anxiety disorder comorbidity on the clinical expression of obsessive-compulsive disorder

BackgroundThe identification of distinct subtypes based on comorbidity offers potential utility in understanding variations in the clinical expression of obsessive-compulsive disorder (OCD). Hence, we examined the hypothesis whether patients with OCD with major depressive disorder (MDD) or anxiety disorder comorbidity would differ from those without in terms of phenomenology.MethodsA total of 545 consecutive patients who consulted a specialty OCD clinic during the period 2004 to 2009 at a psychiatric hospital in India formed the sample. They were evaluated with the Yale-Brown Obsessive-Compulsive Scale (YBOCS), the Mini International Neuropsychiatric Interview, and the Clinical Global Impression scale.ResultsAmong 545 patients, 165 (30%) had current MDD, and 114 (21%) had current anxiety disorder comorbidity. Patients with OCD with MDD were mostly women who had a greater severity of OCD symptoms, more of obsessions (especially religious), greater occurrence of miscellaneous compulsions (need to confess or need to touch), higher suicidal risk, and past suicidal attempts. Patients with OCD with anxiety disorder had an earlier onset of illness that was associated with prior life events, less of compulsions, more of aggressive and hoarding obsessions, pathologic doubts, checking, and cognitive compulsions.ConclusionsObsessive-compulsive disorder, when comorbid with MDD, is more severe and is associated with higher suicidal risk. On the other hand, anxiety disorder comorbidity seems to influence not so much the morbidity but the phenotypic expression of OCD.     

Bipolar co-morbidity in pediatric obsessive-compulsive disorder: clinical and treatment implications

This paper reports on implications of bipolar disorder (BD) co-morbidity in 120 children and adolescents with obsessive-compulsive disorder (OCD) (84 males, 36 females, age 13.7 +/- 2.8 years), diagnosed using a clinical interview according to the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) criteria, and naturalistically followed-up for 12 +/- 6 months. The aim of this naturalistic, retrospective study was to explore the effect of BD co-morbidity, disentangling it from other co-occurring variables, namely the co-morbidity with disruptive behavior disorders. Forty three patients (35.8%) had a bipolar co-morbidity. Compared with OCD patients without BD, they had an earlier onset of OCD, a greater severity and functional impairment, more frequent hoarding obsessions and compulsions, and a poorer response to treatments. They had a higher co-morbidity with attention-deficit/hyperactivity disorder (ADHD) and oppositional-defiant disorder (ODD), and a lower co-morbidity with generalized anxiety disorder (GAD). Finally, they received more mood stabilizers, and 30.2% of them did not receive serotonin-selective reuptake inhibitors (SSRIs) because of pharmacological (hypo)mania. When all the OCD responders and nonresponders were compared, nonresponders (n = 42, 35%) were more severe at baseline and at end of the follow-up, had more frequently hoarding obsessions and compulsions, and had more frequent BD, ODD, and conduct disorder (CD) and less GAD and panic disorder. In the final regression model, hoarding obsessions and compulsions, co-morbidity with ODD, and CD were negative predictors of treatment outcome. This study suggests that even though bipolar co-morbidity is frequent and affects phenomenology and co-morbidity in pediatric OCD, its effect on treatment response seems prevalently accounted for by co-morbidity with disruptive behavior disorders. The significance of the hoarding subtype deserves further research on larger samples of pediatric patients.     

Obsessive-compulsive disorder symptom dimensions show specific relationships to psychiatric comorbidity

The goals of this study were to examine relationships among symptom categories in obsessive-compulsive disorder (OCD), to establish OCD symptom dimensions by factor- and cluster-analytic analyses, and to explore associations between OCD symptom dimensions and comorbid neuropsychiatric conditions. A total of 317 OCD participants underwent a systematic diagnostic interview using the Structured Clinical Interview for DSM-IV. OCD symptoms assessed by the Yale-Brown Obsessive-Compulsive Scale Symptom Checklist (N=169) and by the Thoughts and Behaviors Inventory (N=275) were subjected to factor and cluster analyses. An identical four-factor solution emerged in two different data sets from overlapping samples, in agreement with most smaller factor-analytic studies employing the YBOCS checklist alone. The cluster analysis confirmed the four-factor solution and provided additional information on the similarity among OCD symptom categories at five different levels. OCD symptom dimensions showed specific relationships to comorbid psychiatric disorders: Factor I (aggressive, sexual, religious and somatic obsessions, and checking compulsions) was broadly associated with comorbid anxiety disorders and depression; Factor II (obsessions of symmetry, and repeating, counting and ordering/arranging compulsions) with bipolar disorders and panic disorder/agoraphobia; and Factor III (contamination obsessions and cleaning compulsions) with eating disorders. Factors I and II were associated with early onset OCD. This study encourages the use of cluster analyses as a supplementary method to factor analyses to establish psychiatric symptom dimensions. The frequent co-occurrence of OCD with other psychiatric disorders and the relatively specific association patterns between OCD symptom dimensions and comorbid disorders support the importance of OCD subtyping for treatment, genetic, and other research studies of this heterogeneous disorder.