Aim of this study was to test the hypothesis that obesity promotes the insulin-sensitivity and ovarian hyperandrogenism in anovulating women independently of the polycystic ovary syndrome (PCOS). We examined 80 women of reproductive age (19-38 years, mean 28.5 +/- 0.6 years) with anovulary cycles. 45 subjects had PCOS and 35 had chronic anovulation without hormonal and ultrasound criteria of PCOS. The control group consisted of 12 healthy females with normal ovulary menstrual cycle (age 26.4 +/- 0.6 years). We evaluated plasma insulin level baselines (I0); 120 min after oral administration of 75g of glucose (I120), we examined FSH, LH, prolactin, testosterone, 17 OH progesterone and DHEAS and calculated indexes of insulin sensitivity, i.e. FIRI and G/I. Women with anovulary cycles yielded a significant increase in I0 (p < 0.01), I120 (p < 0.01), FIRI (p < 0.01), FSH, LH (both p < 0.05) and testosterone (p < 0.01), and a significantly decrease in G/I (p < 0.01) in comparison to controls with normal weight. There was a significant correlation between BMI and insulin levels, BMI and FIRI, and between WHR or waist circumference and FIRI, or G/I. The highest levels of insulinemia and the highest degree of insulin resistance were found in obese women (BMI > 30 kg/m2). In the group of obese anovulating women we found a positive correlation between I0 and testosterone (p < 0.01). In PCOS group, we found a negative correlation between I0 and LH (p < 0.01), and FIRI and LH (p < 0.01). In the group of obese PCOS women there were significantly higher levels of plasma insulin, and lower insulin sensitivity as compared to lean PCOS patients. However, lean PCOS women were more hyperinsulinemic and insulin resistant than the control group of lean women. Our results indicate, that obesity is the important factor determinating the insulin sensitivity and hyperinsulinemia in PCOS women. Moreover, the body weight is the major determinant of insulinemia, insulin sensitivity and ovarian hyperandrogenism, independently of PCOS. (Tab. 5, Fig. 4, Ref. 23.).