One hundred and eighty-five patients, whose ages ranged from two to seventy years (mean, thirty years), have been treated at the Mayo Clinic for synovial sarcoma. Sixty-nine per cent of the tumors occurred in the lower extremity: 25 per cent, in the upper extremity; and 6 per cent, in the trunk. Histological characteristics included a predominant bimorphic pattern in 33 per cent of the tumors, a monomorphic pattern in 31 per cent, and a mixed pattern in 36 per cent. For all patients, the five-year survival rate was 38 per cent and the ten-year rate was 23 per cent, with a median survival time of thiry-nine months. However, for those patients treated since 1960, the five-year survival rate was 55 per cent and the ten-year rate was 38 per cent. Female patients had a significantly better survival time than did male patients. Younger patients had a better survival rate, and the prognosis was better for those patients whose tumor were either less than five centimeters in diameter or located in the lower extremity. Survival rates were best for those patients who had wide local excision, but this type of surgery was performed for the lesions that had a more favorable prognosis. A regression study indicated that the size of the tumor was the single most important prognostic variable for survival. Second in importance was the extent of disease on initial presentation, followed by the chronological time of treatment, the age of the patient, and the anatomical site of the tumor.