Hirsutism, which is characterized by excessive growth of terminal hair in a male pattern, is a common clinical condition in women. It may result from various causes including polycystic ovary syndrome, nonclassic adrenal hyperplasia, adrenal or ovarian tumors, or it may be idiopathic. Idiopathic hirsutism (IH) is considered to be one of the most common forms of hirsutism. Although not universal, insulin resistance and hyperinsulinemia have been demonstrated in women with polycystic ovary syndrome. Because there are not enough data showing whether patients with IH also have insulin resistance, we intended to investigate the presence/ absence of insulin resistance in women with IH. Thirty-two women with IH [ mean age, 24.8 +/- 1.2 yr; body mass index (BMI), 24.6 +/- 0.8 kg/m(2)] and 17 healthy women (mean age, 25.8 +/- 0.6 yr; BMI, 22.5 +/- 0.6 kg/m(2)) were included in the study. Eight of 32 patients with IH had BMI higher than 30 kg/m(2). The presence of insulin resistance was investigated by using basal insulin levels, the oral glucose tolerance test, the iv insulin tolerance test, and the homeostasis model assessment(HOMA) score in both groups. Six (18.7%) patients had impaired glucose tolerance (IGT). Overall, patients with IH had significantly (P< 0.05) higher basal insulin levels (10.5 +/- 1.1 mU/liter vs. 5.7 +/- 0.9 mU/liter) and HOMA scores (2.0 +/- 0.2 vs. 1.1 +/- 0.2) and lower plasma glucose disappearance rate values (5.2 +/- 0.2 vs. 6.0 +/- 0.3) than control subjects. However, patients with IGT were notably more obese than the patients with a normal glucose tolerance test. Analyses after omitting the patients with IGT showed that there was still a significant ( P < 0.05) difference in terms of basal insulin levels and HOMA scores. Six of eight (75%) obese patients with IH showed IGT. These data suggest that IH is associated with insulin resistance and an increased prevalence of IGT in obese patients.