Background: Obesity is considered as the risk factor of coronary heart disease, but has been reported to endow better outcome after revasculization. To clarify the relation between obesity and coronary artery disease in acute myocardial infarction (AMI) patients, we examined the extent of coronary artery disease and short-term and long-term outcome after percutaneous coronary intervention (PCI). Methods: 5766 eligible patients (4061 males, 65.0짹12.8 years) enrolled in Korea Acute Myocardial infarction Registry (KAMIR) were classified into 4 groups by WHO body mass index (BMI) criteria: underweight (<18.5 Kg/m2), normal weight (18.5-24.9 Kg/m2), overweight (25-29.9 Kg/m2), obesity (���30 Kg/m2). Results: Hypertension, hypertriglyceridemia, abdominal obesity were more common in overweight/obese patients. High-risk coronary anatomy (significant left main artery and/or significant 3-vessel coronary artery disease) was less often in overweight/obese patients (26.5% vs. 29.5%, p=0.022), although pre-TIMI flow was lower (TIMI 3: 28.3% vs. 32.0%, p=0.008). Overweight/obese patients had lower 1-month major adverse cardiac events (MACE) (9.0% vs. 12.5%, p<0.001) and mortality (3.6% vs. 6.2%, p<0.001). After covariate adjustment, BMI ���25 Kg/m2 still predicted lower MACE (OR, 0.784; CI, 0.631-0.976; p=0.029) and mortality (OR, 0.701; CI, 0.496-0.990; p=0.044). One-year MACE (2.4% vs. 6.2%, p<0.001) and mortality (0.5% vs. 3.3%, p<0.001) were lower in overweight/obese patients. Conclusions: Overweight/obese AMI patients have better short- and long-term outcomes despite of severe coronary artery disease.