Objectives. To review the outcome of men with Stage I nonseminomatous germ cell tumors managed with a policy of active surveillance following orchiectomy. Methods. The clinical records of all men with Stage I nonseminomatous germ cell tumors seen at Royal Prince Alfred Hospital, Australia between 1982 and 1995 were reviewed. Data were obtained concerning the histologic type of tumor, levels of serum tumor markers, relapse and subsequent treatment, and survival. Results. Seventy-seven patients were entered into the active surveillance protocol between 1982 and 1995. With a minimum follow-up of 2 years, 27 (35%) have relapsed, with a median time to relapse of 5 months. Two late relapses occurred at 37 and 57 months after diagnosis. Relapses occurred most commonly in the retroperitoneal lymph nodes, with the lungs the second most common site. Following treatment with chemotherapy and surgery, all patients achieved complete remission, with 1 patient subsequently relapsing and ultimately dying of progressive tumor, One other patient died of acute myeloid leukemia, thought to be secondary to chemotherapy. Overall, 75 patients (97%) remain alive and free of disease. Conclusions. Active surveillance is a safe and effective approach to the management of Stage I nonseminomatous germ cell tumors. Although most relapses occur within the first 2 years, late relapses may occur. (C) 1997, Elsevier Science Inc. All rights reserved.