The pathogenesis of renal scarring after acute pyelonephritis (APN) in children is multifactorial. In addition to well-known risk factors (young age, high grade of vesicoureteral reflux, P-fimbriated Escherichia coli, and treatment delay), a role for genetic predisposition has been suggested. Since the ACE gene deletion polymorphism is a known risk factor for progressive glomerulosclerosis in chronic renal diseases, we have investigated the relationship between the ACE genotypes and the development of renal scarring after APN. Fifty-nine children (43 males and 16 females) with APN diagnosed by urine culture and technetium-99m-dimercaptosuccinic acid ((99)Tc-DMSA) renal scan were studied. ACE genotypes were determined as II, ID, and DD using the polymerase chain reaction technique. A follow-up (99)Tc-DMSA renal scan was performed to evaluate the development of renal scars 3-6 months after treatment. The distribution of ACE genotypes and the allele frequencies were compared in the renal scar-positive ( n=39) and -negative group ( n=20). ACE genotype frequency after stratification by risk factors was also evaluated. The distribution of ACE genotypes did not differ between the renal scar-positive (II 25.9%, ID 35.9%, DD 28.2%) and -negative group (II 35.0%, ID 45.0%, DD 20.0%), before and after stratification by each risk factor. ACE gene deletion polymorphism did not affect the development of renal scar as an independent variable in children with APN.