Finasteride has been used frequently in the treatment of prostate hyperplasia, but this drug inhibits 5alpha-reductase and for this reason could be useful for the treatment of hirsutism. The aim of this study was to evaluate the clinical and hormonal effects of finasteride on hirsute women with idiopathic hirsutism or polycystic ovary syndrome. Twenty-four women were randomly divided into two groups: those given placebo and those given finasteride 5 mg/day. The treatment period was 6 months. All patients were evaluated before the beginning of treatment (baseline) and after 3 and 6 months of treatment using clinical examination through Ferriman-Gallwey score, blood pressure, cardiac frequency and body mass index. Also, we collected blood for hormonal determination of levels of prolactin, 17alpha-hydroxyprogesterone, follicle stimulating hormone, luteinizing hormone, total and free testosterone, dehydroepiandrosterone sulfate, androstenedione and dihydrotestosterone. Furthermore, all patients were asked about their concerns and satisfaction with the treatment. The results showed that the Ferriman-Gallwey score in the 6th month of finasteride treatment was significantly lower than at baseline and the 3rd month of this drug treatment. The dihydrotestosterone level in the finasteride group was also significantly reduced compared to that in the placebo group. The other hormones did not show any statistical difference during the study. All the patients treated with finasteride perceived a reduction in hirsutism after 6 months. In conclusion, our data suggest that finasteride may be effective for the treatment of the hirsute woman with idiopathic hirsutism or polycystic ovary syndrome.