Experience with the management of 128 patients with Stage I testicular seminoma over a 10-year period, 1980-1989, is presented. Fifty-six patients were treated with post-orchidectomy radiation therapy and 72 patients were put on surveillance. Patients thought to be at higher risk of relapse were generally treated with radiotherapy. There have been no tumour related deaths in this series; 5.4% of the irradiated group and 18% of patients on surveillance have relapsed to date. All relapses have been salvaged with further therapy and are currently in complete remission. In this interim analysis, surveillance appears to be a safe alternative to adjuvant radiation therapy provided regular, prolonged follow-up can be ensured. Surveillance is, however, time consuming and resource demanding, and should be undertaken only as part of a formal clinical study. Adjuvant post-orchidectomy radiotherapy should be considered the treatment of choice until further long-term data are available.