To compare the prevalence of the metabolic syndrome using the National Cholesterol Education Program (NCEP) and the International Diabetes Federation (IDF) definitions and to contrast the association between the prevalence of cardiovascular disease and the metabolic syndrome using both definitions in the Korean population, we used data from the 2001 Korean Nation Health and Nutrition Survey, which is a nationally representative survey of the noninstitutionalized civilian population. The age-adjusted prevalence of the metabolic syndrome was 18.8%+/-0.5% (men, 17.8%+/-0.8%; women, 20.5%+/-0.7%) using the NCEP definition and 19.5%+/-0.5% (men 15.0%+/-0.8%, women 23.9%+/-0.7%) using the IDF definition among participants 20 years or older. The agreement rate, which is the percentage of participants who were classified as either having or not having the metabolic syndrome by both definitions of the metabolic syndrome, was 84.6%+/-0.5% (kappa=0.54). The prevalence of the metabolic syndrome using the NCEP definition was higher in participants with lower body mass index, whereas the prevalence using the IDF definition was higher in subjects with higher body mass index. The odds ratio (OR) for coronary artery disease was 3.5 (95% confidence interval [CI], 2.0-6.1) for participants with the metabolic syndrome defined by the NCEP definition, whereas it was 2.8 (95% CI, 1.6-5.0) for those with the metabolic syndrome defined by the IDF definition. Similarly, the OR for stroke was higher using the NCEP definition (OR, 3.0; 95% CI, 1.7-5.2) compared with that of the IDF definition (OR, 2.3; 95% CI, 1.3-4.0). However, the CIs by both definitions overlapped considerably. In conclusion, the prevalence of the metabolic syndrome using the IDF definition was higher than that using the NCEP definition, whereas the NCEP definition was more closely associated with cardiovascular disease in the Korean population.