From 1965 through 1988, 113 patients affected with testicular seminoma were treated at the Dept. of Radiotherapy, University "La Sapienza", Rome, Italy. Mean age of the patients was 38 years; in 70 cases tumor developed in the right testis and in 43 in the left one. In 9 patients underlying cryptorchidism was observed. All cases underwent radical orchiectomy. Histology diagnosed anaplastic seminoma in 5 cases and pure seminoma in all the other patients. Structures were involved in 7 cases. Eighty-four patients were in stage I, 20 in stage IIA, 4 in IIB, 4 in IIIA, and 1 in stage IIIB. All patients staged as I and IIA were treated with exclusive radiotherapy on paraaortic lymph nodes and inguinal and iliac lymph nodes of the involved sites (total doses: 28-35 Gy in stage I and 34-40 Gy in... stage IIA). Before 1970 these patients underwent prophylactic irradiation of mediastinum and of left supraclavicular lymph nodes (total dose: 25-28 Gy). Patients in stage IIB were administered subdiaphragmatic lymph nodes irradiation with inverted-Y field (total dose: 36-45 Gy). Two cases were irradiated also on mediastinum and left supraclavicular lymph nodes, and 2 received two cycles of polychemotherapy (PVB) before irradiation. Patients in stage IIIA underwent sub-/supra-diaphragmatic irradiation (total dose: 40-45 Gy, and 40-42 Gy). The case in stage IIIB underwent palliation chemotherapy and local irradiation. All cases in stages I, IIA and IIB obtained complete remission. Three cases of the 4 in stage IIIA obtained complete remission (75%), while 1 (25%) progressed and died 8 months after diagnosis; the only case in stage IIIB progressed and died after 7 months of follow-up. Two cases in stage I recurred (2.4%), 1 in the mediastinum and 1 in the left supraclavicular lymph nodes. Both were cured with salvage radiation therapy. Toxicity related to treatment was low. Two cases in stage I developed secondary malignant neoplasms, at 4 and 34 months of follow-up, respectively.