Five years ago, the use of preoperative chemotherapy for Wilms' tumor was adopted at this institution. Thirty children ranging in age from 5 months to 9 years had histologically confirmed Wilms' tumor (needle biopsy, n = 26; open biopsy, n = 4). Stage was determined by chest and abdominal computed tomography (CT) scan. Bilateral tumors were present in 6 children. All children received actinomycin D and vincristine from 3 weeks to 6 months before surgery. Seven children with bilateral tumors or stage IV disease also received adriamycin. CT-measured tumor masses shrunk in most cases. Subsequently, nephrectomy was performed in 23 patients and partial nephrectomy in 4, 2 of whom had bilateral disease. In 2 patients, residual bilateral well-differentiated epithelial tumor was not surgically resected. One child died before surgery. Reevaluation at delayed total or partial nephrectomy resulted in a downstaging of disease in 12 (41%). Further chemotherapy and radiation was based on the surgical stage. Postoperative chemotherapy (4 months to 2 years) was administered to all patients. The chest and/or abdomen were radiated in 12. Four patients (13%) died, 1 of radiation pneumonitis and 3 of the disease progression (2 with unfavorable histology, 1 of whom had bilateral disease). Two of 4 with unfavorable histology and 4 of 6 with stage IV disease have survived. It is concluded that this preoperative chemotherapy protocol is as effective as the National Wilms' Tumor Study (NWTS) protocol. The treated tumor is smaller, less friable, and easier to remove. Furthermore, because of downstaging, less radiation is necessary for cure.