The polycystic ovary (PCO) syndrome is frequently associated with obesity. That subset of women reportedly shows a much higher incidence of hirsutism and menstrual irregularities than do nonobese women with PCO syndrome. We evaluated the clinical features and hormonal profiles of 56 women with PCO syndrome and correlated them with the presence or absence of obesity. Thirty-eight (67.8%) of these women were obese (body mass index > or = 25 kg/m2). While presenting with the classic manifestations of PCO, they did not differ significantly from the manifestations of nonobese women with PCO syndrome. Although obese women with PCO had a lower incidence of oligomenorrhea as compared to nonobese women with PCO (57.9% vs. 83.3%, respectively) and amenorrhea was more frequent in the former group (42.1% vs. 16.6%, respectively), these findings are not statistically significant. The incidences of hirsutism and anovulatory infertility in the obese group as compared to the nonobese group were 81.6% vs. 77.8% and 28.9% vs. 27.8%, respectively (not statistically significantly different). The mean (+/- SE) serum levels of luteinizing hormone (LH), follicle stimulating hormone (FSH), LH/FSH ratios, prolactin and testosterone were not statistically significantly different among the two groups. The present study found that obesity is common in PCO syndrome but that there are no significant differences in the clinical and hormonal characteristics of obese and nonobese women with it. Further studies are warranted to clarify the impact of obesity on clinical, metabolic and hormonal changes in PCO syndrome.