PURPOSE: 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. MATERIALS AND METHODS: 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. RESULTS: 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). CONCLUSIONS: This pilot study demonstrates that early use of anticholinergic therapy in infants with high voiding pressures and/or small bladder capacity after primary posterior urethral valve ablation has beneficial effects on bladder function.