This study was conducted to investigate whether the length of the interval between a urinary tract infection and the performance of the voiding cystourethrogram influences the presence or severity of vesicoureteral reflux (VUR). In this study 161 children with first episode of urinary tract infection were evaluated. Depending on time of performance of voiding cystourethrogram (VCUG), patients divided into two groups: early (within the first 7 days following treatment) and late (during second week or thereafter of the start of treatment). The prevalence and severity of vesicoureteral reflux in both groups were compared. Out of 161patients, the early and late groups consisted of 75 and 86 patients, respectively. The prevalence of vesicouretral reflux in the early and late groups was 25.3% and 30.2%, respectively. No significant difference was observed between two groups regarding prevalence (P=0.598) and severity (P=0.379) of vesicoureteral reflux. This study showed that the prevalence and severity of VUR is not affected by timing of VCUG. Therefore, it is recommended that in children with urinary tract infection, VCUG should be done following negative urine culture as soon as possible.