Advances in molecular genetics have resulted in the identification of several forms of autosomal dominant polycystic kidney disease (PKD). Cystic kidneys have also been observed in tuberous sclerosis, von Hippel-Lindau syndrome, oro-facial-digital type I syndrome, Hajdu-Cheney syndrome, Ehlers-Danlos syndrome, and an "overlap" connective tissue disorder, and cannot be distinguished by ultrasonography from PKD. We have studied four children with similar cystic kidneys. None had a family history of PKD. One child has osteogenesis imperfecta type IV, two appeared to have a mild Ehlers-Danlos syndrome, and the fourth has inguinal hernias and undescended testes. We speculate that polycystic kidneys may occur in connective tissue dysplasias. We also realize that these may be chance associations with spontaneous mutations for PKD.