OBJECTIVE - The aim of this study was to explore the prevalence and pattern of the metabolic syndrome and its association with hyperinsulinemia in an urban Korean population of 269 men and 505 women. RESEARCH DESIGN AND METHODS - The National Cholesterol Education Program Adult Treatment Panel (ATP) III guidelines were used to calculate the sex-specific prevalence of the metabolic syndrome. After excluding individuals taking medication for hypertension, diabetes, or dyslipidemia, we used factor analysis to examine the pattern of the metabolic syndrome in 206 men and 449 women. RESULTS - The prevalence of metabolic syndrome was 16.0% in men and 10.7% in women aged 30-80 years. However, ATP III criteria for central obesity are not optimal for an Asian-Pacific population; when waist circumference is reduced from 102 to 90 cm in men and 88 to 80 cm in women, the prevalence of the metabolic syndrome increased to 29.0 and 16.8%, respectively. Sex-specific factor analysis showed four factors in men (obesity, glucose intolerance, hypertension, and dyslipidemia) and three in women (obesity-hypertension, glucose intolerance, and obesity-dyslipidemia). Insulin resistance estimated from fasting insulin levels clustered with three of the four factors in men and two of the three factors in women. By ATP III or Asian-Pacific waist circumference criteria, the prevalence of the metabolic syndrome increased with increasing tertiles of insulin resistance, which was estimated by a homeostasis model assessment. CONCLUSIONS - The metabolic syndrome is common in an urban Korean population when using Asian-Pacific waist criteria. The prevalence of the metabolic syndrome increased with increasing tertiles of insulin resistance.