Eighty-four patients with clinical Stage I non-seminomatous germ-cell testicular tumours were entered into a prospective study after orchiectomy to evaluate a policy of close surveillance without lymph node irradiation or node dissection; 16 (19%) have manifested evidence of metastatic disease and received chemotherapy. All patients in the study are alive, 3 of the 16 relapsing patients are receiving chemotherapy and the 13 who have completed it are in complete remission at 4 to 43 months (mean 21). Relapses were diagnosed at 2 to 8 months (mean 5.3 months) after orchiectomy and were not invariably associated with elevated serum markers. The relapse rate was significantly higher for malignant teratoma undifferentiated (MTU) primary tumours than malignant teratoma intermediate (MTI) (40.7 and 6.8% respectively) and preliminary data suggest that the association of MTU with vascular invasion places the patient at high risk of relapse. Pre-orchiectomy serum marker status was not a significant prognostic factor. Despite sub-optimal surgical management in 11/84 patients no example of scrotal recurrence has been encountered. It is concluded that a rigorously monitored policy of close surveillance after orchiectomy is a feasible and successful method of management in Stage I testicular non-seminoma. Further experience should allow patients requiring immediate post-orchiectomy chemotherapy to be identified.