Twenty-six cases of a pure seminoma of the testis that had been treated by postoperative radiotherapy have been reviewed. The overall 5-year survival rate was found to be 92.3%. Further, no severe adverse effects, including sterility, was found. Prophylactic mediastinal radiation is considered to be unnecessary, because supradiaphragmatic lymph node metastasis was seen in only 1 patient, who has remained disease-free 4.5 year after the treatment of a recurrence. Extranodal metastasis was seen 5 cases, 2 of these cases showing bone metastasis that was successfully treated, thereby achieving complete remission. A seminoma is considered to be one of the most curable malignant diseases, however, long-term follow up is a necessity since stage 1 seminoma has been found to show a generalized dissemination after a 16-year, disease-free interval.