Sixty-three children with persistent nocturnal enuresis were urodynamically assessed and subsequently treated with oxybutynin chloride. Urodynamic evaluation, including graduation of detrusor instability and comparison of maximum bladder capacity with the age-predicted norm, confirmed an inadequate storage function in 84% of the children. Treatment benefit totaling 70%was dependent upon urodynamic findings, with best relation to the determined bladder capacity. The value attributed to graduation of uninhibited contractions was prognostic in accordance with further subdivision of the maximum bladder capacity. Treatment benefit was limited in children with normal urodynamic findings.