Polycystic ovary syndrome (PCOS) is characterized by insulin resistance and consequent hyperinsulinemia. Insulin resistance also plays an important role in the metabolic syndrome (MS). We conducted a cross-sectional study to determine the prevalence of the MS in young Korean women with PCOS and whether it is associated insulin resistance. One hundred and seventeen young women with PCOS (age: 26+/-5, 16-39 years) were evaluated for the frequency of MS according to the modified Adult Treatment Panel III. Total testosterone (T), free T, androstenedione, dehydroepiandrosterone sulfate (DHEAS) and sex hormone binding globulin (SHBG) were measured, and insulin sensitivity was evaluated by euglycemic hyperinsulinemic clamp technique. The prevalence of MS in women with PCOS was 14.5%, nearly 3.5-fold higher than in age-matched women in Korean urban population (4.3%) [J.-Y. Oh, Y.-A. Sung, Y.S. Hong, E. Barrett-Conner, Prevalence and factor analysis of metabolic syndrome in an urban Korean population, Diabetes Care 27 (2004) 2027-2032]. The most frequently occurring component of MS was low HDL cholesterol (45%), and the least frequent was high fasting serum glucose level (0.9%). PCOS women with MS had significantly higher free T, and lower SHBG compared with those without MS. And women with MS showed significantly lower M-value and higher fasting/post-glucose load insulin levels. M-value was still significantly lower in women with MS even after the adjustment for BMI. MS is frequent in young Korean women with PCOS and it reflects more severe insulin resistance. These results suggest the importance of early and regular screening of metabolic disturbance in even young women with PCOS.