Thirty-six of 39 previously untreated evaluable patients with advanced metastatic seminoma (stage greater than or equal to IIb) obtained a complete response (CR) and three a partial response (PR) after cisplatin-based combination chemotherapy with or without surgery/radiotherapy (group 1). After a median observation time of 36 months, 33 patients are alive with no evidence of disease (NED). Fifteen additional patients received cisplatin-based chemotherapy due to relapsing seminoma after initial radiotherapy (group 2). Thirteen patients obtained a CR, and two a PR. Patients from group 1 lived significantly longer after the start of chemotherapy than those from group 2. The rate and severity of the treatment-related complications were comparable in both groups. The most frequent nonfatal side effects of cisplatin-based combination chemotherapy were Raynaud-like phenomena, polyneuropathy, and myelosuppression. Four patients developed fatal complications (septicemia, bone marrow aplasia). In three of 12 patients with evaluable postchemotherapy histology, vital malignant seminoma was found. Cisplatin-based combination chemotherapy in advanced seminoma patients is highly effective, but includes a significant risk of severe complications. Less toxic treatment regimens should be explored, at least for patients who have less advanced tumors (stage IIb/limited stage IIc).