We reviewed retrospectively 40 children seen from 1980 to 1984 with vesicoureteral reflux in 53 ureters. All patients had a hyperreflexic bladder on urodynamic evaluation with or without vesicoperineal dyssynergia but they were otherwise neurologically normal. All except 1 child received prophylactic antibiotics. Of the children 37 received oxybutynin therapy for bladder hyperreflexia for 3 to 18 months. Reflux disappeared or became grade I in 62.3 per cent of the ureters. Of the children manifesting urinary incontinence at the time of urodynamic study reflux disappeared or became grade I in 78.6 per cent. Reflux resolved or became grade I in 20 per cent of the children with no urinary incontinence. Of those patients with recurrent reflux at the onset of urinary incontinence and bladder instability reflux resolved or became grade I in 80 per cent. Oxybutynin therapy for hyperreflexic bladder resulted in an average increase in bladder capacity of 97 cc (54.2 per cent), which was maintained after cessation of treatment. These data suggest that bladder instability can be an important factor in causing and perpetuating reflux. Therapy aimed at decreasing intravesical pressure will enhance resolution or downgrading of reflux.