Objective: The new definitions for metabolic syndrome (MS) proposed by the IDF and revised NCEP have caused some confusion because patients have emerged that have satisfied the revised NCEP but not the IDF criteria. We performed this study to compare the prevalence of these criteria and to investigate the characteristics of discrepant cases. Research design and methods: A total of 7962 individuals aged X 20 years (3597 men; 4365 women) who participated in the 1998 Korean NHANES were included. We assessed the agreement between the revised NCEP and IDF criteria and investigated the characteristics of cases satisfying the revised NCEP criteria but not the IDF criteria. Results: The prevalence of MS by the revised NCEP (25.7% of men and 31.9% of women) was higher than that according to the IDF (14.2% of men and 26.6% of women). The IDF criteria failed to identify 44.9% of men and 16.6% of women identified as having MS according to the revised NCEP criteria. The discrepant group showed more adverse metabolic profiles and unfavorable lifestyles despite lower waist circumference as compared with those having MS by both the IDF and revised NCEP criteria. The prevalence of discrepant cases was higher among the elderly. Conclusions: The IDF criteria were inferior to the revised NCEP criteria in identifying the metabolically abnormal but nonobese groups known to be predisposed to type 2 diabetes and cardiovascular disease. Further research regarding the appropriateness of central obesity as an obligatory criterion proposed by the IDF seems to be warranted.