Ninety-one children with nocturnal enuresis or enuresis plus daytime urgency incontinence were studied by cystometry. Seventy-two per cent of the girls and 62 per cent of the boys had evidence of bladder instability. Sixty-eight children in whom abnormalities were found on preliminary voiding urodynamics or voiding cystourethrography also underwent calibration and endoscopic examination under anesthesia. An atropine-suppression test was also performed preoperatively in some children with a markedly unstable bladder demonstrated on preoperative cystometry. In the majority of children tested suppression of bladder instability with atropine was demonstrable. Voluntary detrusor sphincter dyssynergia was demonstrated in a majority of the children with daytime urgency incontinence. Sixty-five per cent of the boys and 81 per cent of the girls were treated for urethral obstructive lesions suspected to be of functional urodynamic significance. Postoperative cystometry showed marked improvement in bladder stability in 57 per cent of the girls and 63 per cent of the boys treated for suspected urethral obstructive pathology. The anticholinergic suppression test was found to have no significant predictive value relative to the cause or surgical curability of bladder instability. The pathophysiologic significance of overactivity of integral voiding reflexes 6 through 11 is described.