Cyclic voiding cystourethrography (CVC) enhances the detection of vesicoureteric reflux (VUR). We investigated whether more-severe VUR may be overlooked, and whether older children are at risk of having their VUR missed with the conventional single-cycle study. Three hundred and seventy patients, 168 boys and 202 girls aged 1 month to 16 years, consecutively admitted over 1 year for suspicion of VUR, underwent two complete cycles of filling and voiding CVC. One hundred and four subjects, 33 boys and 71 girls, were older than 3 years (mean age 5.7 years, range 3.2-16 years). Sixty-six refluxing ureters from 51 patients were identified in the first cycle and 61 refluxing ureters from 45 patients were identified only with the second cycle. Four instances of grade IV VUR in 4 patients and three of grade V VUR in 3 patients were overlooked completely in the first cycle. Seven episodes of VUR < or = grade III from 5 patients diagnosed in the first cycle were upgraded to > or = grade IV at the second cycle. The presence of VUR was identified only in the second cycle in 35 of 74 subjects aged < or = 3 years and in 10 of 22 aged > 3 years (not significant). Of the 10 children aged > 3 years, 2, who had diagnosis only at the second cycle, had > or = grade IV VUR. More-severe VUR may be overlooked or down-graded in a single-cycle study. Two-cycle CVC is also useful in children older than 3 years.