Thirty-six cases of synovial sarcoma (13 biphasic and 23 monophasic) were subjected to a clinicopathologic study that included electron microscopy and immunohistochemistry. The group consisted of 21 males and 15 females ranging in age from 2 to 63 years. The majority of tumors (27 cases) were found in the hip and lower extremity. Immunohistochemical study revealed that keratin, which was detected in 92% of the biphasic and 57% of the monophasic tumors, was a more sensitive marker of epithelial differentiation than EMA or CEA. The overall 5-year survival of the patients was 64%. Male sex, older age, presence of tumor necrosis, monophasic pattern, and absence of keratin positivity had an unfavourable effect on survival but lacked statistical significance. Survival was significantly lower in patients with tumors exhibiting more than 15 mitoses per 10 HPF (P less than .02) and in those with tumors showing necrosis and a mitotic rate greater than 5 mitoses per 10 HPF (P less than .005).