OBJECTIVE To measure serum resistin levels in women with polycystic ovary syndrome (PCOS) and assess possible correlations of resistin to the hormonal and metabolic parameters of the syndrome. METHODS Clinical study. METHODS University hospital. METHODS Ninety selected women were classified as follows: group I: 35 anovulatory women with PCOS (body mass index [BMI] >25 kg/m(2)); group II: 35 anovulatory women with PCOS (BMI <25 kg/m(2)); group III: 20 ovulating women (controls) without hyperandrogenemia (BMI <25 kg/m(2)); women of group III were volunteers. METHODS Blood samples were collected between the 3rd and the 6th day of the menstrual cycle of the ovulating women, and between the 3rd and the 6th day of a spontaneous bleeding of the anovulatory women, at 9 a.m., after an overnight fast. METHODS Serum levels of FSH, LH, PRL, 17alpha-hydroxyprogesterone, sex hormone-binding globulin, androgens, insulin, resistin, and glucose. RESULTS Resistin levels were found to be significantly increased in group I compared with those of group II and those of group III. No significant difference in resistin levels was found between groups II and III, despite significant differences in insulin levels and the glucose-to-insulin ratio. Multiple regression analysis showed that resistin levels do not correlate with any parameter independent of BMI. CONCLUSIONS Based on the above findings, we presume that resistin is unlikely to be a major determining factor of PCOS-associated insulin resistance and is not actively involved in the pathogenesis of the syndrome.