In 1973, Perlman et al described a familial syndrome of bilateral renal hamartomas with or without nephroblastomatosis, macrosomia, islet cell hypertrophy, unusual facies, and early lethality. Two additional sibs were recently reported by Neri et al . We report on two sibs with polyhydramnios, fetal ascites, and abdominal muscular hypoplasia, visceromegaly, and subsequent development of Wilms tumor in one of them. Delineated features of this syndrome include visceromegaly, macrosomia, renal hamartomas, nephroblastomatosis, cryptorchidism in males, unusual facial appearance, polyhydramnios, fetal ascites, and Wilms tumor but do not include hemihypertrophy, omphalocele or umbilical abnormalities, aniridia, or other conditions known to be associated with Wilms tumor. This condition should be considered primarily in the differential diagnosis of fetal ascites without hydrops and possibly in the differential diagnosis of familial Wilms tumor, polyhydramnios, congenital hepatomegaly, or nephromegaly.