The long-term survival of patients with synchronous bilateral Wilms tumor is not well defined. Retrospective review of 185 patients registered with the National Wilms Tumor Study from January 1974 to July 1986 with stage V tumors suggests that the long-term outcome remains good. Over-all survival is 83%, 73% and 70% at 2, 5 and 10 years, respectively. Unfavorable histology, age at diagnosis and the most advanced stage of the individual tumors remain the most important prognostic variables. No significant difference in survival was noted between patients undergoing initial surgical resection of the tumor and those managed with initial tumor biopsy followed by chemotherapy with or without radiotherapy and subsequent surgical resection. Survival does not appear to be compromised by attempting to conserve native renal function with renal-sparing operations.