OBJECTIVE: To examine the clinical efficacy of low dose spironolactone in hirsute women. DESIGN: Retrospective. SETTING: Outpatient endocrinology clinic. PATIENTS: One hundred nine consecutive women prescribed 75 to 100 mg/d spironolactone for at least 4 months in whom adequate follow-up data were available. RESULTS: Hirsutism improved in 72% of the women. Women with regular menses, whether or not they used oral contraceptives (OCs), had the highest response rate to spironolactone (78%), whereas women with irregular menses who did not use an OC had the lowest response rate (55%). Favorable responses were associated with increased severity of hirsutism (P = 0.04) and lower serum dehydroepiandrosterone sulfate levels (P = 0.05). Responders and nonresponders did not differ significantly in age (P = 0.10), duration of hirsutism (P = 0.14), pretreatment serum testosterone (T) (P = 0.48), or body mass index (P = 0.11). However, when each parameter was divided into subsets, trends toward decreasing response were observed with increasing age, duration of hirsutism over 15 years, and increasing serum T level. CONCLUSION: Low-dose spironolactone improves hirsutism in a majority of hirsute women, irrespective of age, severity or duration of hirsutism, menstrual status, or serum hormone levels.