A series of 136 cases of tendosynovial sarcomas were studied from the histologic point of view. All of the primary, recurrent and metastatic tumors were reclassified according to histologic type, anatomic site and size; age and sex of patients and modality of surgical treatment. The overall 5-year survival rate was 40%. Among the factors which most favorably influenced the prognosis were: small size (74%, 5-year survival), "exposed" primary site (53%, 5-year survival), and histologic type (biphasic form: 55%, 5-year survival and epithelioid sarcoma: 58%, 5-year survival). Children and elderly patients had also better than the average prognosis. Sixty percent of the sarcomas recurred after wide local excision. Twelve percent of the tumors metastasized to regional lymph nodes and 10% to bones. Almost all of the 24 patients who were autopsied died because of cardio-pulmonary insufficiency due to massive pleuropulmonary metastasis. It is hoped that better understanding of the natural history of these tumors will lead to optimal local and systemic therapy and better survival.