A patient with Werner's syndrome and osteosarcoma presenting as scleroderma.

Werner's syndrome (WS) is often mistaken for scleroderma. We describe a patient with WS who presented with an enlarging, painful mass of the right knee that proved to be a juxtaarticular osteosarcoma of the distal femur. Recognition of WS and prompt investigation of any painful, enlarging masses to exclude sarcomatous degeneration will benefit these patients.