OBJECTIVES: Insulin resistance is a major pathophysiology in polycystic ovary syndrome (PCOS), and assessment of insulin sensitivity is important. Various insulin sensitivity indices from fasting state or oral glucose tolerance test (OGTT) have been compared with euglycemic hyperinsulinemic clamp. We aimed to evaluate the usefulness of these indices in young Korean women with PCOS. METHODS: Euglycemic hyperinsulinemic clamp test and 75 g OGTT were performed in 290 women with PCOS. Insulin mediated glucose uptake (IMGU), the insulin sensitivity index from clamp, was compared with various insulin sensitivity indices such as composite insulin sensitivity index (ISIcomp), estimated metabolic clearance rate (MCRest) of glucose and estimated insulin sensitivity index (ISIest), area under the curve of glucose and insulin ratio (AUC-GIR), OGTT-derived Belfiore index, and oral glucose insulin sensitivity index (OGSI) by Kazama. Fasting state indices such as glucose insulin ratio (GIR), homeostasis model assessment for insulin resistance (HOMA-IR), fasting Belfiore index, and quantitative insulin sensitivity check index (QUICKI) were also compared with IMGU. RESULTS: The correlation coefficients of ISIcomp, MCRest, ISIest, AUC-GIR, OGTT-Belfiore index, and OGSI with IMGU were all about 0.5 (Ps'<0.001) in PCOS women as a whole. The MCRest and ISIest were significantly correlated with IMGU in both obese (r=0.58 and 0.58, P<0.0001) and non-obese subjects (r=0.33 and 0.32, P<0.001). Fasting glucose and insulin-derived indices showed worse correlation with IMGU than OGTT-derived ones. CONCLUSION: The MCRest and ISIest from OGTT might be the best replacement for the insulin sensitivity index from hyperinsulinemic euglycemic clamp independent of obesity.