The influence of obesity on sex hormone-binding globulin (SHBG) and androgen concentrations in hirsute and nonhirsute women has been evaluated. The study was performed in 226 hirsute women (88 obese and 138 non-obese) classified as being affected by polycystic ovarian syndrome (PCOS) or by idiopathic hirsutism (IH) and in 100 nonhirsute control women ([C] 60 lean and 40 obese). SHBG, free testosterone (fT), androstenedione (A), estradiol (E2), dehydroepiandrosterone sulfate (DHEAS), and gonadotropin levels were measured during the first week of the menstrual cycle by radioimmunoassay (RIA). A significant negative correlation between SHBG and body mass index (BMI) was observed in PCOS, IH, and C women. In obese women--whether PCOS, IH, or C-fT levels were significantly higher and, conversely, SHBG levels were lower than in non-obese women. A negative correlation between SHBG and fT was evidenced in each group. Upper-body obesity was associated with lower SHBG and higher fT levels than lower-body obesity. In conclusion, obesity, particularly upper-body obesity, is associated with a reduction in SHBG and an increase in fT in both nonhirsute and hirsute women.