The Brazilian Wilms Tumor Study Group has registered 16 cases of synchronous bilateral Wilms tumor since 1986, of which 14 were available for analysis. Most patients were treated according to a prospective trial in which bilateral renal preservation was emphasized. Overall survival was 79% (11 of 14 cases), and both kidneys were preserved in 57% (8 of 14) of the patients with synchronous disease. Of the 14 patients 5 had undergone at least 3 surgical procedures. In 10 cases in which pathological reports were available for review residual disease was documented in 5 but none had relapse.