Hirsutism is a common symptom of women affected by polycystic ovary syndrome (PCOS). The effectiveness of the antiandrogen flutamide alone was studied in 25 patients affected by PCOS with severe hirsutism for a period of 24 months. Seventeen of these patients had not been treated before and eight had had previous but unsatisfactory therapy. Nineteen patients showed a normal body weight (BMI < 25 kg/m2) whereas six were obese (BMI > 35 kg/m2). A chemical and endocrinological evaluation and an assessment of the degree of hirsutism, assigned by Ferriman-Gallwey score (mean 22 +/- 3.038), was performed under baseline conditions. Patients started treatment with flutamide (Eulexin, Schering-Plough, Kenilworth, USA) at the dose of 500 mg daily. A chronobiological assessment of gonadotropin episodic secretion and of gonadotropin response to GnRH challenge (10 micrograms in bolus) was done before and on day 7 of flutamide administration. During treatment, our patients showed a marked and significant reduction of hirsutism starting from a score of 6 and reaching the maximum (9.6 + 2.1) at 24 months of therapy. No relevant hormonal changes or side-effects were observed during therapy. Our data demonstrate that hirsutism in PCOS can rapidly and markedly respond to treatment with flutamide alone without important side-effects even if administered for a long period.