Insulin resistance and hyperinsulinemia play important roles in the pathogenesis of polycystic ovary syndrome (PCOS). In addition, some women with PCOS have been shown to have insulin secretory defects and can be predicted to be at an increased risk for glucose intolerance. We performed the present study to determine the prevalence and risk factors for glucose intolerance in Korean women with PCOS. We consecutively recruited 194 women with PCOS diagnosed by American Society for Reproductive Medicine/European Society of Human Reproduction and Embryology (ASRM/ESHRE) criteria. Anthropometric measures, 75 g oral glucose tolerance test (OGTT), and measurement of insulin sensitivity (insulin mediated glucose uptake; IMGU) using euglycemic hyperinsulinemic clamp technique were performed. In women with PCOS, the prevalence of impaired glucose tolerance (IGT) and/or impaired fasting glucose (IFG) was 17.0% and type 2 diabetes 1.0%, and in lean women with PCOS, the prevalence of IGT and/or IFG was 5.9%. The prevalence of glucose intolerance was 28-fold higher in women with PCOS, and 9.8-fold higher in lean women with PCOS compared to age-matched Korean women. Women with glucose intolerance had higher BMI, waist circumference, free testosterone, fasting insulin, 2-h post-load insulin, total cholesterol, LDL cholesterol, triglyceride and lower sex hormone binding globulin and IMGU than women with normal glucose tolerance (NGT) (P < 0.05). IMGU was the most powerful predictor for glucose intolerance after adjustment for age, BMI, waist circumference, and hyperandrogenemia. The 2-h OGTT was the best screening measure for glucose intolerance and diagnosis of diabetes in women with PCOS. Young Korean women with PCOS have high prevalence for glucose intolerance and type 2 diabetes, and insulin resistance is the most important factor associated with glucose intolerance.