BACKGROUND: Obesity is associated with decreased insulin sensitivity, atherogenic dyslipidemia and hypertension, but clinical studies have also identified a "metabolically healthy" obese phenotype. OBJECTIVE: To compare the characteristics of so-called "metabolically healthy" obese (MHO), normal weight subjects (MHNW) and obese with insulin resistance in a nationally representative sample in the United States. DESIGN, SETTING AND PARTICIPANTS: Insulin resistance was defined by a homeostatic model assessment (HOMA) value in the upper tertile for the entire NHANES cohort. "Metabolic health" was defined as the absence of diabetes, insulin resistance, metabolic syndrome, and lipid-lowering therapy. The study evaluated the 314 MHO, 1173 MHNW and 843 insulin-resistant obese from among the 6485 non-diabetic, nno-pregnant adults aged 20-79 years, who participated to the United States National Health and Nutrition Examination Survey, 1999-2004. MAIN OUTCOME MEASURES: Demographic, metabolic, nutrition and physical activity features. RESULTS: MHO and MHNW groups were similar regarding age, and fasting glucose and triglyceride levels. MHO had higher insulin (P<0.0001), insulin resistance as measured with the homeostatic model (p<0.0001), non-HDL cholesterol (P=0.002 in females and P=0.049 in males) and C-reactive protein levels (P<0.0001 in females and P=0.038 in males), and lower high-density lipoprotein cholesterol (HDL) levels (P<0.002). In addition, MHO females had higher low-density lipoprotein (LDL) cholesterol levels (P=0.012) and systolic blood pressure (P=0.02), and lower intake of dietary fiber (P=0.0009) and levels of physical activity (p=0.002). Triglycerides levels were normal in the MHO group. CONCLUSIONS: "Metabolically healthy" obese people have multiple dysmetabolic changes that may signal increased risk for coronary artery disease.