A total of 40 women presenting with polycystic ovary syndrome (PCOS) and excessive body weight/obesity were randomly allocated to 3 groups. The patients in group 1 were advised to change the life style (including consumption of a low-calory diet and regular physical exercises), those making up group 2 had to change the life style and take metformin (850 mg twice daily), the patients of group 3 used metformin without modifying their life style. Thirty three patients completed the study. Those in groups 1 (n=14) and 2 (n=10) experienced a similar significant reduction of both the body weight and the HOMA index. In group 3 (n=9), these characteristics remained virtually unaltered. The fraction of women displaying the positive menstrual response during the treatment was not significantly different in groups 1 and 2 (50 and 60% respectively; p=0.77) whereas none of the patients in group 3 showed the positive menstrual response (the difference between this and the two previous groups was significant; p=0.035). A significant decrease in the testosterone level was documented in the women of group 2. The authors conclude that it was the reduction of the body weight rather than regular intake of metformin at a daily dose of 1700 mg that contributed to the improvement of the menstrual function in women with PCOS and the excessive body weight.