['Abnormal bladder function following posterior urethral valve ablation can lead to deleterious effects on renal function and urinary continence. We performed a pilot study to determine if bladder dysfunction could be ameliorated by the early administration of oxybutynin.', 'We enrolled infants who underwent primary posterior urethral valve ablation by the age of 12 months. On initial urodynamics patients demonstrating high voiding pressures (greater than 60 cm H(2)O) and/or small bladder capacity (less than 70% expected) were started on oxybutynin. Urodynamics and ultrasound were performed every 6 months until completion of toilet training, at which time oxybutynin was discontinued.', 'Oxybutynin was started in 18 patients at a mean age of 3.4 months and was continued for a mean of 2.2 years. Urodynamics revealed that initial high voiding pressures improved from a mean of 148.5 to 49.9 cm H(2)O in 15 of 17 patients. All 8 patients with initially poor bladder compliance demonstrated improvement on oxybutynin. All 7 patients with initially low bladder capacity (mean 47.7% expected bladder capacity) demonstrated improvement while on oxybutynin (mean 216% expected bladder capacity).'] Does early administration of oxybutynin improve bladder function and clinical outcomes in newborns with posterior urethral valves?