Vesicoureteric reflux (VUR) is known to occur in families. In siblings of index patients with VUR, there is a much higher incidence (16% to 46%) than in the general population. The renin-angiotensin system plays an important role in renal development. Recently, it has been reported that angiotensin-converting enzyme (ACE) I/D gene polymorphism is a risk factor for renal parenchymal damage in patients with congenital urological abnormalities. The aim of this study was to investigate the ACE I/D genotype pattern in familial VUR patients. Blood samples were obtained from 86 families in which two or more members had VUR. Samples of DNA were extracted from 407 blood samples (183 affected patients and 224 non-affected family members). To detect ACE I/D polymorphism, polymerase chain reaction (PCR) amplification was performed using specific primers for the ACE gene. PCR products were electrophoresed with 2% agarose gel containing ethidium bromide. Among 224 non-affected family members the ACE genotype distribution of DD, ID, and II was 23%; 56% and 21%, respectively. The ACE genotype distribution of 183 affected patients was 28%, 47% and 25%, respectively. There was no significant difference in ACE I/D distribution between affected patients and their non-affected families. Both the ACE genotype distribution of affected patients and that of non-affected family members were not significantly different from the previously reported genotype distribution of the normal Caucasian population. This study demonstrates that ACE genotype frequencies are similar in index patients with VUR and their unaffected siblings, thus suggesting that the ACE gene is not involved in the development of familial VUR.