A review of 105 children with urinary tract infection showed an increasing prevalence of grades II-III vesicoureteric reflux with diminishing age. During infancy reflux was almost always severe, and affected boys as often as girls. Radiologically scarred kidneys were drained by refluxing ureters in 98% of cases. The prevalence of scars also rose significantly with increasinglyly severe reflux. Deterioration of existing scars or new scar formation was seen in 15 children; 18 out of 20 affected kidneys (90%) were associated with grade III vesicoureteric reflux. 2 out of 5 children who developed new scars did so after 5 years of age. Because severe reflux may occasionally be seen in the presence of a normal intravenous urogram, and since the finding of grades II-III vesicoureteric reflux is an indication for chemoprophylaxis, we consider cystourethrography essential in children of all ages with recurrent urinary tract infection. In children under 5 years the increased prevalence of both severe reflux and renal scarring are arguments for regarding cystourethrography as a necessary initial investigation.