BACKGROUND The aim of this study was to determine the effects of independent prognostic variables, such as prechemotherapy tumor markers, the extent of disease at diagnosis, the tumor markers postchemotherapy (PC), and the pathology of the PC residual mass on the overall survival of patients with primary mediastinal nonseminomatous germ cell tumors (PMNSGCT). METHODS The authors undertook a retrospective review of 39 patients with PMNSGCT between 1983 and 1997 who received their initial chemotherapy at Indiana University and 36 additional patients referred for PC resection. All patients received chemotherapy based on the combination of cisplatin and etoposide. The median follow‐up was 22 months (range, 12–144 months). RESULTS The prechemotherapy tumor markers did not affect overall survival. Extent of disease (mediastinal only vs. visceral metastases) was an important prognostic factor for survival in univariate analysis (P = 0.042). Sixty‐two of 75 patients underwent PC resection of residual disease. Fifteen of the 62 patients achieved a CR with chemotherapy alone, as the PC resection revealed only necrosis. Fourteen of these 15 patients continuously had no evidence of disease (NED). Forty‐seven of the 62 patients had NED with chemotherapy and PC resection, including 31 with teratoma and 16 with carcinoma. However, 11 of 31 with teratoma and 11 of 16 with carcinoma subsequently relapsed. Although 18 patients had elevated tumor markers at the time of PC resection, 6 of 18 had only necrosis and 4 had teratoma. The PC tumor markers did not affect survival. The pathology of the resected specimen was the most significant predictor of survival in multivariate analysis (P < 0.001). CONCLUSIONS Twenty‐eight of 39 patients (71.8%) with PMNSGCT treated at Indiana University achieved NED status, but only 16 (41%) continuously had NED. Twenty of 36 (55.5%) referred for resection continuously had NED. Disease confined to the mediastinum and necrosis in the PC specimen were important prognostic factors for survival. Cancer 2000;88:1051–6. © 2000 American Cancer Society.