A prospective study was established to identify the incidence of vesicoureteral reflux in the siblings of patients with reflux. Of 78 patients with reflux 104 siblings were screened with an awake voiding cystogram and 34 (32 per cent) were found to have reflux. Of these 34 siblings 25 (73 per cent) had no abnormal voiding symptoms or history of urinary tract infection. The highest incidence of reflux was found in the siblings of those patients with radiographic evidence of renal scarring. Early detection and followup in this high risk group may be a vital tool in determining more about the natural history of vesicoureteral reflux and its relationship to renal damage.