Background. -Acute pyelonephritis can induce parenchymal scarring. The aim of this study was to evaluate the usefulness of procalcitonin (PCT) to predict renal involvement in febrile children with urinary tract infection (UTI). Methods. -In a prospective study serum PCT was measured and compared with others commonly used inflammatory markers in children admitted to the emergency unit with acute pyelonephritis. Renal parenchymal involvement was assessed by a 99mTc-labeled dimercaptosuccinic acid (DMSA) renal scar performed in the first 3 days after the admission. Results. -Among 42 enrolled patients, 19 (45%) had acute renal involvement (Group A) ; 23 (55%) (Group B) had normal DMSA scan (n = 16), or old scarring (n = 4) or various anomalies related to uropathy (n = 3). In group A, the mean PCT level was significantly higher than in the group B (5,4 ng/ml, vs 0,4 ng /ml, p < 10-5). In these 2 groups, mean C reactive protein (CRP) levels were 99,1 mg/l and 44,6 mg/l respectively (p < 0,001). For a level of serum PCT ≥0,5 ng/ml, the sensitivity and specificity to predict the renal involvement were 100%and 87%respectively; for a level ≥20 mg/l CRP had a sensitivity of 94%but a specificity of 30%. Conclusion. -Serum PCT levels were significantly increased in febrile children with UTI when acute renal parenchymal involvement was present. PCT seems a better marker than CRP for the prediction of patients at risk of renal lesions. Acute pyelonephritis can induce parenchymal scarring. The aim of this study was to evaluate the usefulness of procalcitonin (PCT) to predict renal involvement in febrile children with urinary tract infection (UTI). Methods. -In a prospective study serum PCT was measured and compared with others commonly used inflammatory markers in children admitted to the emergency unit with acute pyelonephritis. Renal parenchymal involvement was assessed by a 99mTc-labeled dimercaptosuccinic acid (DMSA) renal scar performed in the first 3 days after the admission. Results. - Among 42 enrolled patients, 19 (45%) had acute renal involvement (Group A); 23 (55%) (Group B) had normal DMSA scan (n = 16), or old scarring (n = 4) or various anomalies related In group A, the mean PCT level was significantly higher than in group B (5,4 ng / ml, vs 0,4 ng / ml, p <10-5). In these 2 groups, mean C reactive protein (CRP) levels were 99,1 mg / l and 44,6 mg / l respectively (p <0,0 01). For a level of serum PCT ≥ 0.5 ng / ml, the sensitivity and specificity to predict the renal involvement were 100% and 87% respectively; for a level ≥ 20 mg / l CRP had a sensitivity of 94% but a specificity of 30%. Conclusion. Ser PCT PCT levels were significantly increased in febrile children with UTI when acute renal parenchymal involvement was present. PCT seems a better marker than CRP for the prediction of patients at risk of renal lesions.