From 1968 to 1996, 21 of 97 (22%) patients with Wilms tumor treated at the University of Iowa Hospitals and Clinics relapsed after initial therapy. The most common sites of initial recurrence were the lungs in 12 (57%), abdomen in 3 (14%), bone in 3 (14%), and liver in 2 (10%). Treatment for recurrence included chemotherapy in 16, radiotherapy in 15 and surgery in 8. Radiotherapy was given to bilateral lungs of 8 previously untreated chests; total dose was 1,200 cGy to 1,500 cGy, with 2 patients receiving 1,000-cGy boost. One patient had abdominal radiotherapy after surgery for relapse; six patients had palliative radiotherapy to distant sites. The 1-, 3-, and 5-year postrelapse survivals were 62 +/- 11%, 38 +/- 11%, and 33 +/- 10%, respectively. Using Cox proportional-hazard regression models, abdominal recurrence (p = 0.0002; hazard ratio, 39.5) and initial stage IV disease (p = 0.019; hazard ratio, 6.27) were found to have a negative impact on postrelapse survival. Seven patients with previously nonirradiated chests are alive at a median follow-up of 123 months after relapse (range, 55--272 months); all had whole lung irradiation with or without chemotherapy at relapse for lung metastases. Radiotherapy was also found to be an effective treatment in the palliation of painful metastases.