An 8-year-old boy with an uncorrected ventricular septal defect, pulmonary stenosis, mental retardation, and gigantism died 24 hours after partial resection of a large right-sided Wilms' tumor. The presence of other abnormalities, including a small umbilical hernia and overgrowth of the external genitalia, raises the possibility that this case represents a variant of the Beckwith-Wiedemann syndrome. The typical facial features of Sotos' syndrome were not present. Gross examination of the surgical specimen revealed that tumor was present in the resected margin of left renal vein. Necropsy showed that death resulted from extensive cerebral infarction due to occlusion of the left internal carotid artery and its branches by tumor emboli. Paradoxical embolism had occurred during or soon after partial resection of the tumor mass due to passage of tumor fragments into the systemic circulation through the ventricular septal defect.