The purpose of this study was to estimate the prevalence of 'metabolically obese, but normal-weight' (MONW) and 'metabolically healthy, but obese' (MHO) phenotypes in Korean adults and identify the characteristics and health behaviors related to both phenotypes. Of the 5267 participants (2227 men, 3040 women) from the 3rd Korean National Health and Nutrition Examination Survey, the MONW phenotype (8.7% of total subjects, 12.7% of normal-weight subjects) was defined as individuals of normal weight (BMI<25) with the metabolic syndrome (MS), and the MHO phenotype (15.2% of total subjects, 47.9% of obese subject) was defined as obese individuals (BMI>or=25) without the MS. The odds ratio for MONW phenotype was significantly higher for those at older age, those with lower education, those who had moderate alcohol consumption, and time spent participating in moderate-intensity exercise. The odds ratio for MHO phenotype was significantly lower for those at older age, men, those with lower education, and former/current smokers. In conclusion, regardless of weight status, health behaviors should be modified to prevent MS.