BACKGROUND Interleukin (IL)-8 acts as a potent neutrophils chemoattractant responsible for the migration of neutrophils into the infected renal tissue to protect against invading pathogens. The aim of this study was to assess the role of IL-8 on acute-phase pyelonephritis and later renal scarring in children. METHODS A total of 124 children with a first-time febrile urinary tract infection (UTI) were studied. The diagnosis of acute pyelonephritis was confirmed by Tc-dimercaptosuccinic acid (DMSA) renal scan. Serum and urine samples were obtained from 124 children with UTI and 20 healthy children for IL-8 measurement. RESULTS The 124 children were divided into acute pyelonephritis (n = 70) and lower UTI (n = 54) groups according to the results of DMSA scans. The initial serum and urine IL-8 values of children with acute pyelonephritis were significantly higher when compared with lower UTI and healthy controls (all P < 0.001). Renal scarring was seen in 26 (38.8%) of these 67 children with acute pyelonephritis at follow-up DMSA scans. Both the initial serum and urine IL-8 concentrations were significantly higher in children with renal scarring than in those without (both P < 0.001). The mean age of children with renal scarring was also significantly lower than those without scarring (P = 0.004). Multivariate analysis showed that the highest initial IL-8 values, age <20 months and reflux grades > or =III all were independent predictors of renal scarring. CONCLUSIONS Those children younger than 2 years of age with the highest IL-8 concentrations during the acute phase of pyelonephritis as well as children with reflux grades of III or greater are at a high-risk for developing renal scarring in the future.