The aim of this study was to compare the clinical efficacy and safety of low dose cyproterone acetate-estrogen combination (Diane(R)) and the 5 alpha-reductase inhibitor finasteride in the treatment of hirsutism. Fourty-two women with hirsutism were included in the study. Twenty-one patients treated with cyproterone acetate (CPA) 2 mg and ethinyl estradiol (E) 35 mu g daily on days 5-25 of the menstrual cycle, 21 with finasteride 5 mg daily. Hirsutism score, hormone levels, multiscreen blood chemistry and side effects were evaluated at three-monthly intervals for 9 months. A significant decrease in hirsutism score as compared to baseline was observed after 9 months with either CPA+E (Diane(R)) (mean +/- SE, 15.81+/-1.19 vs 8.38+/-1.21) or finasteride treatment (17.81+/-1.05 vs 10.86+/-0.91) (p<0.0005). The reductions in hirsutism scores (mean% +/- SE) were 14.23+/-2.29 vs 19.77+/-2.22 (p<0.05) at 3, 40.23+/-4.58 vs 29.49+/-2.69 (p<0.02) at 6 and 50.99+/-4.13 vs 39.87+/-3.30 (p<0.02) at 9 months in CPA+E and finasteride groups, respectively. No significant changes were observed in hormone levels during finasteride treatment. Serum free testosterone significantly decreased at the third month of treatment, and remained suppressed for the duration of treatment in CPA+E group. DHEAS levels also decreased significantly after 6 and 9 months of therapy with CPA+E. SHBG significantly increased during CPA+E treatment. We conclude that both drugs are effective and well tolerated, but CPA+E appears to be more effective than 5a-reductase inhibitor finasteride in long-term treatment of hirsute women. Diane(R) is also a cost-effective drug. (J. Endocrinol. Invest. 21: 348-352, 1998) (C)1998, Editrice Kurtis.