Thirty-three patients with a non-seminomatous germ cell tumor of the testis in clinical stage I were treated only by orchidectomy. The very careful follow-up--with tumor marker assays every 3 weeks, chest X-rays every 6 weeks and CT-scans of the lungs and retroperitoneum every 3 months--revealed metastases in 7 of the patients (21%). All these relapses were diagnosed within 6 months of the orchidectomy. Para-aortic node metastases were found in 5 of the 7 patients, with additional inguinal node metastases in 1 and additional lung metastases in 1; 2 patients had only lung metastases. Six of the 7 patients with a relapse were given chemotherapy (PVB); 1 patient refused chemotherapy. In view of residual disease a surgical excision was performed; it revealed necrosis as well as mature teratoma. All 33 patients are still alive, the post-orchidectomy follow-up period being 12-38 months.