Over 50% of women with polycystic ovary syndrome (PCOS) have been reported to have varying degree of insulin resistance and it may contribute to hyperandrogenism. The aim of the study is to identify whether the insulin resistance is present in non-obese Korean women with PCOS and whether the phenotype is different according to insulin sensitivity. Seventy-three non-obese (BMI<23 kg/m(2)) women with PCOS and 34 age and BMI comparable control women with regular menstrual cycles were examined. Standard 75 g OGTT was performed to determine the status of glucose tolerance. Insulin sensitivity was measured by euglycemic hyperinsulinemic clamp technique. The fasting plasma glucose (p<0.01) and post-glucose load plasma insulin (p<0.01) of women with PCOS were higher than those of controls. Glucose disposal rate (M-value) was lower in women with PCOS compared to controls (p<0.05). Insulin resistant (IR) and insulin sensitive (IS) PCOS were divided by the M-value of 25-percentile (5.5mg/kg min) in controls. Between IR and IS groups, DHEAS (p<0.01), post-glucose load plasma insulin (p<0.05) showed differences after the adjustment for BMI. Our non-obese women with PCOS showed significant insulin resistance compared to their age and BMI comparable control subjects and their insulin resistance may contribute to hyperandrogenism especially via adrenal androgen overproduction.