From April 1975 through May 1981, 51 patients had teratoma resected from residual disease following cisplatin-based combination chemotherapy. All patients had normal serum markers before resection of abdominal (25), lung (12), mediastinal (5), thoracoabdominal (8) or other (1) disease. Teratoma was classified as mature in 29 cases, immature in 15 or immature with nongerm cell elements in 7. Of the 51 patients 31 (61 per cent) remain free of recurrent disease, while 20 either had recurrent carcinoma (10) or teratoma (10) requiring further therapy. Nine patients died, including 1 in whom angiosarcoma developed, which was thought to be secondary to previous radiation therapy. In 4 patients the initial relapse of carcinoma developed beyond 2 years after resection. Univariate factors predicting for relapse include tumor burden, immature teratoma with nongerm cell elements and site (mediastinum), while only immature teratoma with nongerm cell elements and site predicted for survival. Patients with immature teratoma had a comparable relapse-free and over-all survival as those with mature teratoma. Using a multivariate analysis, primary tumor site at the mediastinum was the most significant adverse factor predictive for relapse and survival. This study appears to support the various pre-clinical models that demonstrate multipotential capabilities of teratoma. Complete surgical excision of teratoma remains the most effective treatment with continued close followup recommended for high risk patients (immature teratoma with nongerm cell elements, large tumor burden and primary mediastinal tumors) with resected teratoma.