The definitive cure rate for clinical stage 1 testicular seminoma is very close to 100%, and prophylactic irradiation of the regional lymph nodes is associated with a low morbidity. Nevertheless, in recent years a "wait-and-see" policy has been proposed by some researchers. We analysed the cost/benefit ratio of radiotherapy (RT) by review of the case histories of 299 patients treated at the Department of Radiotherapy of the Istituto Nazionale per lo Studio e la Cura dei Tumori in Milan from January 1968 to December 1989. The 5-year overall survival was 99% (97.5% at 10 years), while the 10-year disease-free survival was 96%. The recurrence rate was 2.3%, but no patient relapsed in the irradiated areas. Acute toxicity was very moderate with only 4 (1.3%) serious radiation sequelae occurring 6 to 27 years after treatment. However, 9 second malignancies (3%) were observed. Lastly, we have calculated the costs for our National Health Service comparing surveillance policy and prophylactic irradiation.