Excellent treatment results have been achieved historically with postoperative radiotherapy in testicular seminoma. In this retrospective study the treatment results of 211 patients with Stage I-II testicular seminoma treated in Finland during the years 1970-1983 were evaluated. 176 (84%) patients received postoperative radiotherapy alone. In addition to radiotherapy, 26 (12%) patients received chemotherapy during the primary treatment. There were 129 Stage I (61%), 66 Stage IIA-B (31%) and 16 Stage IIC (8%) tumors. The 5-year survival rate was 95% in Stage I, 87% in Stage IIA-B and 73% in Stage IIC. In Stage I, seven relapses (relapse rate 6%) occurred after irradiation; three of them were cured with second-line therapies. None of the relapses occurred within the radiotherapy field. In Stage IIA-B, 31 patients had only parailiacic + aortic irradiation, 25 patients received both parailiacic + aortic and mediastinal irradiation. With both radiotherapy techniques there was no significant difference in the number of relapses (seven and three) and in the remission rate (94% and 96%). Radiotherapy alone was used on four Stage IIC patients and one of them died during the primary treatment. Two of them relapsed, but could be cured with chemotherapy. These results correspond to those reported in the literature and they suggest that prophylactic mediastinal irradiation is unnecessary in Stage IIA-B patients. Stage IIC patients should receive chemotherapy initially.