Thirty-one adults with Wilms tumor were reported to the National Wilms Tumor Study from 1968 to 1979. Treatment and survival data for these patients were analyzed and compared to similar information derived from children enrolled in the first National Wilms Tumor Study. The ages of the 31 adults ranged from 17 to 63 years (mean 29 years). All but 3 patients had surgical resection or excision of tumor, 7 did not receive postoperative irradiation and all but 1 had chemotherapy. Actinomycin D and vincristine were the drugs used most commonly, 26 of the 31 patients receiving both agents. Advanced disease at diagnosis (6 stage III and 9 stage IV versus 9 stage I and 5 stage II--in 2 cases stage was not known) was found more often than in children in whom stages III and IV disease made up 27 per cent of the first National Wilms Tumor Study population. The 3-year actuarial survival rate for the 31 adults was 24 per cent: 48 per cent for stages I and II disease and 11 per cent for Stage IV disease. Comparable data for children in the first National Wilms Tumor Study, adjusted for stage, were 74, 87 and 53 per cent, respectively. It is concluded that adults with Wilms tumor treated as were these have a worse prognosis than children managed according to the first National Wilms Tumor Study regimen. However, those adults in this series who were treated aggressively, that is surgical excision, postoperative irradiation and multi-agent chemotherapy, appeared to have fared better than adults treated in the pre-chemotherapy era. It is concluded that aggressive therapy should be given to all adults with Wilms tumor irrespective of stage.