Renal transplantation as part of the treatment for Wilms tumor was done on 20 patients. In 80 per cent the neoplasms were bilateral. Transplantation is indicated in individuals whose renal function is severely impaired or absent because of the malignancy, treatment or both. Patients who received homografts less than a year after treatment of the tumors had a 47 per cent incidence of recurrence or metastases compared to a zero incidence of these problems in those whose transplants were delayed for longer periods. Survival for 2 years or more was obtained in 75 per cent of the recipients with unilateral neoplasms and in 38 per cent of the patients with bilateral tumors.