To study the effects of incontinence surgery on detrusor contractility, a group of 24 women who preoperatively voided without a detrusor contraction during voiding urethrocystometry were re-evaluated for detrusor contractility three months after surgery for stress urinary incontinence. Twelve women regained detrusor contractility during voiding and were able to resume spontaneous voiding after incontinence surgery. The remaining 12 patients, representing true detrusor atony, continued to void without a detrusor contraction, and the majority (10/12) needed prolonged postoperative bladder drainage prior to resumption of spontaneous voiding. Presence of reduced flow rates and absence of detrusor contraction during preoperative voiding indicated true detrusor hypotonicity. Two thirds of the patients voiding with normal flow rates but without a detrusor contraction during preoperative voiding regained detrusor contraction after incontinence surgery (p less than 0.05).