We investigated angiotensin converting enzyme gene (ACE I/D) polymorphism as a risk for progressive renal damage in congenital uropathies. The ACE I/D genotype was determined in 196 Caucasian patients with congenital uropathies and 163 individuals with no clinical or sonographic evidence of any urological malformations. The study group included patients with ureteropelvic junction obstruction (n=49), primary obstructive megaureter (n=19), primary vesicoureteral reflux (VUR) (n=67), and posterior urethral valves (n=27). Thirty-four patients were excluded because of additional diseases or insufficient follow-up. There was no difference in the ACE I/D distribution between children with uropathies and normal controls (II 16%, ID 56%. DD 28% vs. II 26%, ID 50%, DD 24%). Renal lesions were found in 99 of 162 children by ultrasonography, intravenous pyelography, and nuclear scans. In these children there was significant over-representation of the DD genotype (II 11%, ID 53%, DD 36%) compared with normals (P<0.005, X2=14.9) or with patients with uropathies but no renal lesions (II 23%, ID 62%, DD 15%, P<0.005, X2=14.9). Because ACE I/D has been linked with progressive deterioration of renal function, we evaluated a subset of patients with initially normal kidneys who developed radiographic renal lesions (n=28). Among these patients there was an even greater over-representation of the DD genotype (II 0%, ID 43%, DD 57%, P<0.001, X2=22.6) compared with patients with uropathies but no radiographic lesions. Multivariate analysis revealed that the DD genotype is a risk factor for parenchymal destruction, which was independent of time of diagnosis, surgical intervention, or urinary tract infection. This finding was particularly relevant in patients with VUR who constituted the majority with initially normal kidneys who developed radiographic damage (22/28). Indeed, the odds ratio of developing parenchymal damage with VUR was significantly increased if the individual had the DD genotype (4.2, 95% confidence interval 1.4-13.0). In conclusion the ACE I/D gene polymorphism is a risk factor for renal parenchymal damage in patients with congenital urological abnormalities and appears particularly relevant in children with VUR, where it is an independent predisposing factor.