A retrospective review was undertaken of 66 boys with posterior urethral valves with regard to incidence and prognostic significance of vesicoureteric reflux. The results indicate that: Regardless of the age of the patient, the existence of bilateral reflux at the time of presentation implies a worse prognosis than does unilateral or no reflux. Reflux which does not stop spontaneously after the valves have been destroyed is generally associated with a functionless and often dysplastic kidney; surgical cure of such reflux is therefore pointless. Reflux stops spontaneously after valve ablation when the involved kidney possesses useful function; surgical cure of reflux is therefore unnecessary. In some cases, however, it remains possible that reflux may continue to damage the kidney during the interval between relief of the urethral obstruction and spontaneous cure of the reflux. Nevertheless, the grossly dilated refluxing ureter is poor surgical material and it is concluded that the best chance of preserving renal function in the majority of boys with urethral valves and reflux lies in endoscopic fulguration of the valves, controlling infection and awaiting spontaneous reflux cure.