Ovarian hyperandrogenism is a common disorder of women of reproductive age. The therapies that are presently available to treat this disorder are not uniformly effective or free of adverse effects. We conducted a prospective study of eight women receiving ketoconazole for a mean duration of 44 ± 15 (SEM) weeks, as therapy of ovarian hyperandrogenism. Serum testosterone and hair growth rate declined in patients while on 600 to 1,000 mg ketoconazole daily. Menses normalized in seven of eight subjects during treatment. Ketoconazole therapy was not associated with a change in basal or postgonadotropin-releasing hormone stimulation gonadotropin levels. Basal cortisol levels were also unchanged on ketoconazole though responsiveness of cortisol to adrenocorticotropic hormone stimulation tended to be reduced. We conclude that ketoconazole can effectively reverse the biochemical and clinical abnormalities of ovarian hyperandrogenism. Until the issue of its safety is resolved, ketoconazole therapy is best limited to select individuals who agree to careful monitoring and the use of reliable birth control methods during treatment.