An analysis was performed to determine whether a cranial reduction of the portals to the T11/T12 junction instead of the common T10/T11 junction would alter the outcome of patients with stage I seminoma. Of 163 consecutive patients with newly diagnosed testicular seminoma referred to the authors' institution between April 1992 and April 1999, 80 patients with stage I seminoma were treated with cranially reduced para-aortic treatment fields reaching from the top of T12 to the bottom of L4. Median total dose was 20.0 Gy (range, 19.8-27.2 Gy). Patients were followed-up by the use of CT in regular intervals. After a median follow-up of 7.1 years (range, 4.1-11.1 years), four patients (5%) had relapsed resulting in an actuarial 5-year relapse-free survival of 95%. No patients relapsed within the cranially reduced treatment volume above the top of T12. The cranial reduction of the para-aortic treatment fields resulted in a median reduction of treatment volume of 16% (range, 13-21%). The achieved median reduction in treatment volume of 16% appears to be relevant and is not associated with an increased relapse rate. This approach is recommended in analogy to the surgical approach in NSGCT to further minimize the risk of radiation-related late effects.