Thirty-six patients with apparent stage I nonseminomatous germ cell tumor (NSGCT) of the testis were treated by inguinal orchidectomy and intensive follow-up only. Assessment included measurement of serum alpha fetoprotein (alpha FP) and beta human chorionic gonadotropin (beta HCG) (tumor markers) and chest x-ray monthly for 1 year, then twice monthly for 1 year, with computed tomographic (CT) scans of abdomen and chest repeated three times monthly for the first year and six times monthly for the second year. Median follow-up was 36 months (range, 14 to 92 months). Relapse occurred in 12 patients (33.3%) at a median of 7 months (range, 2 to 28 months). Elevated markers were of limited importance in relapse detection, confirming the need for close clinical and radiological follow-up. Of nine histological factors examined in the primary tumor only the presence of lymphatic invasion was associated with a significantly higher relapse rate. All patients were treated at relapse with cisplatin-based chemotherapy. Four underwent surgery in addition, two before and two after chemotherapy. Eleven were rendered disease-free, but four had a second relapse. One patient has died, one is alive with disease, and ten are disease-free. Chemotherapy failed to cure six patients who had relapsed but bulk of disease was not a factor. Despite the good overall result reported here, optimal postorchidectomy management of apparent stage I disease remains to be defined.