A randomized, double-blind, placebo-controlled study of the efficacy of prazosin hydrochloride for the treatment of stress incontinence in women. Prazosin hydrochloride, an alpha1-adrenoceptor antagonist, was evaluated for the treatment of urinary incontinence in women. We studied 80 women, randomly assigned to receive prazosin hydrochloride (n = 30), or placebo (n = 30) or no treatment (n = 20) for 1 year. Bladder neck mobility and urethral closure pressure profiles were obtained at baseline and at 6 and 12 months. All patients filled out daily voiding diaries for 1 year. At 12 months there was a significant improvement in incontinence episodes and pad weight, favoring prazosin hydrochloride (P < 0.05); there was no difference between prazosin hydrochloride and placebo. Diary variables improved significantly at 1 year (P < 0.05) for prazosin hydrochloride but not for placebo. The mean increase in bladder neck mobility was 3.3 mm with prazosin hydrochloride and 5.3 mm with placebo. There were no serious adverse effects. Prazosin hydrochloride had a beneficial effect on stress incontinence but did not improve urethral function. Long-term effects should be further investigated in placebo-controlled trials.