Sixty-two consecutive patients with clinical stage I nonseminomatous testicular cancer were entered into a prospective study to receive no treatment after orchiectomy until clinical evidence of recurrent disease. Of 59 evaluable cases, 41 (69.5%) remained continuously disease free for a median duration of 30 months (range, 18 to 46 months), and evidence of metastatic disease developed in 18 patients (30.5%) from 2 to 36 months after orchiectomy. The median disease-free interval for relapsing patients was 6 months. Retroperitoneal metastases developed in ten patients; seven patients had pulmonary metastases, and one patient had progressive elevation of the serum alpha-fetoprotein level. Relapses were significantly more frequent in patients with either embryonal carcinoma, infiltrating testicular cancer (pT greater than 1), peritumoral vascular invasion, or in those who underwent transscrotal biopsy. One patient with relapse refused salvage therapy and died. The remaining 17 patients have been rendered disease free with cisplatin combination chemotherapy and/or surgery. However, two patients showed further recurrence, with one in the lung and the other one also in the retroperitoneal nodes. In our opinion, surveillance following orchiectomy will provide useful information in clinical stage I nonseminomatous testicular cancer, but it is a difficult study. For the time being, it should be restricted to specialized centers only. In the meanwhile, retroperitoneal lymphadenectomy remains the standard treatment.