PURPOSE: To determine (1) the relationship between the cortical defects seen on 99 mTc-DMSA renal scans and age, and (2) the presence and degree of vesicoureteral reflux, and then to depict the risk factors for cortical defects in children with acute urinary tract infection (UTI). Furthermore, to assess the diagnostic value of VCUG in predicting a defect on 99 mTc-DMSA renal scans. MATERIALS AND METHODS: We studied 134 kidneys in 67 children aged 15 days-10 years (M:F=39:28) in whom symptomatic UTI was present. In all these children, both DMSA renal scans and voiding cystourethrography (VCUG) were performed. Scanning took place within 7 days of diagnosis and VCUG was performed after one month of diagnosis. Scintigraphic findings were graded according to the extent and number of cortical defects. We evaluated the relationships between the cortical defects seen on DMSA scans and age, and the grade of vesicoureteral reflux. The diagnostic value of VCUG in predicting cortical defects was analysed. Results: The prevalence of cortical defects was greater in patients older than two years (38/54, 70%) than in those aged less than two (38/80, 48%). The frequency of cortical defects was related to vesicoureteral reflux (p<0.05) and grade of reflux (p<0.05). As this latter increased, the extent of cortical defects also increased (p<0.05), and DMSA scans revealed the presence of these in 76 of the 134 kidneys (57%) with acute UTI. In 30 of these 76 (39.5%), VCUG demonstrated the presence of vesicoureteral reflex. On the other hand, vesi-coureteral reflex was found in 36 of the 134 kidneys (27%), and in 30 of these 36 (83%), cortical defects were noted. The sensitivity of VCUG in predicting cortical defect was 39.5%, while specificity was 89.7%. The positive predictive value for defects was 83.3%, and the negative predictive value was 53.1%. The relative risk of cortical defect in the presence of vesicoureteral reflux was 1.78. CONCLUSION: Renal cortical defects are significantly related to age and grade of vesicoureteral reflux. Risk factors for developing cortical defects were older age (> or =2yrs) at the time of acute UTI, and high grade of vesicoureteral reflux. The specificity of VCUG in predicting cortical defects is relatively high but the sensitivitiy is low, and a significant proportion of cortical defects therefore occurred in the absence of vesicoureteral reflux.