Objective We hypothesized that Korean subjects with normal weight obesity (NWO) are at risk of diabetes mellitus (DM). Methods Cross-sectional study including 774 men and 1,200 women aged 19~64 years from the 2008 Korean National Health and Nutrition Examination Surveys (KHANES) was carried out. NWO was defined by 18.5 kg/m2 ≤ BMI < 23 kg/m2 with the highest tertile gender-specific percentiles of body fat (BF) ( > 23.4% for men and > 34.6% for women). BF was measured using dual-energy X-ray absorptiometry (DXA). DM was classified by fasting blood glucose ≥ 126 mg/dL or treatment of the disease. Dietary intakes, food consumption, and life habits were evaluated. Results The prevalence of NWO was < 3.5% in men and 6.5% in women. NWO men had higher diastolic blood pressure and NWO women had higher total cholesterol than those of lean men and women had, respectively. When compared with the low BF group, the prevalence of diabetes in the subjects with NWO men was 2.5-fold (odds-ratio 2.54 [1.63~10.21]), which was similar with over-weight men (odds-ratio 2.3 [1.12~5.01]). NWO women had higher prevalence of DM (odds-ratio 1.92 [1.20~4.30]) than lean women but not overweight women (odds-ratio 2.71 [1.33~5.51]). NWO subjects showed a low physical activity practice, and consumed less fruits and dairy products. Conclusion NWO might be associated with physical activity, low quality of diet, and DM. Detailed screening for NWO might be necessary to prevent and/or early detect DM.