The aim of this study was to evaluate the acute and late effects of irradiation in 56 patients with stage I and II testicular seminomas. A retrospective study of patients' records was performed paying attention to the acute and late toxicity of radiation in relation to treatment fields and radiation doses. Treatment groups were compared using the χ2-test. Mild to moderate nausea and/or vomiting was seen in 66% of patients and occurred equally independent of the treatment volume or radiation dose. Increased bowel frequency was seen in 59% and was more common when a larger treatment volume was used. Skin reactions increased with increase in treatment volume and dose (p = 0.046). Severe late complications were recorded in two patients (myocardial damage - 1/4 at risk, duodenal ulcer - 1/56 at risk). These could not be attributed solely to the irradiation as other contributing factors might play a role. Overall the data suggest that the risk of major posttreatment morbidity is minimal for patients with testicular seminoma treated with postoperative radiotherapy.