Obesity is a traditional risk factor for the development of cardiovascular disease. However, recent studies have described a better outcome of obese patients in the clinical course of acute coronary syndromes.We investigated the impact of the body mass index (BMI) on occurrence and outcome of acute ST-elevation myocardial infarction (STEMI). Data of 10 534 consecutive patients with STEMI of the German MITRA PLUS registry were analyzed, comparing international classes of the BMI (obesity: BMI >or= 30 kg/m(2), overweight: 25-29.9 kg/m(2), normal weight: 18.5-24.9 kg/m(2)).STEMI occurred at a younger age in obese patients. The obese patients with first STEMI were 3 years younger than the normal weight patients with first STEMI (62.5 vs 65.7 years, p <0.0001).After STEMI has occurred, the obese patients had the lowest hospital (6.0%) and long-term mortality (4.8%) of all compared BMI-groups. In a multivariate analysis, obesity compared to normal weight was associated with a trend of a reduced mortality without significance during the hospital course (OR 0.81, 95% CI 0.60-1.08) and with significance during follow-up (OR 0.56, 95% CI 0.40-0.79).In conclusion, our data show that obesity is a risk factor of a manifestation of STEMI at a younger age compared to normal weight patients. After STEMI has occurred, obesity is associated with a trend of a lower mortality during the following clinical course. Therefore, the focus of prevention should be the reduction of obesity and metabolic syndrome in young people, to avoid the early occurrence of STEMI by primary prevention.