The authors examined the effect of three months' treatment with spironolactone in 34 women with polycystic ovary syndrome. In all patients a significant decrease in hirsutism was noted as well as restoration of a regular although anovulatory menstrual pattern. Plasma luteinizing hormone and follicle-stimulating hormone levels remained unchanged after spironolactone treatment; however, prolactin levels were lowered in both women with normal and those with elevated basal levels. Plasma testosterone, androstenedione, and dehydroepiandrosterone sulfate levels were decreased after three months of therapy. No side effects were observed. Plasma electrolytes and liver function tests were normal during the entire time of treatment. This therapy is recommended as initial nontoxic but effective treatment for women with polycystic ovary syndrome who are hirsute and have menstrual disturbances.