Obesity is an independent risk factor for coronary artery disease and premature death. However, a number of studies have demonstrated that it is inversely associated with short-term mortality in patients with acute coronary artery disease. Most data suggesting this “obesity paradox” identify obesity with body mass index (BMI), but weight was not previously considered while it could be an alternative measurement that may also prove to be an accurate predictor of in-hospital mortality. The aim of this study was to determine whether BMI and weight are related to in-hospital mortality in patients admitted for an acute coronary syndrome (ACS). Data was derived from the EURHOBOP cohort, a multicenter ACS hospital registry conducted between 2008 and 2010 in 7 European countries. ACS patients with discharge diagnosis of myocardial infarction or unstable angina were included. Socio-demographic characteristics, medical histories and acute episodes at entry or during hospitalization were recorded. In-hospital mortality risk by BMI or weight categories were assessed using multiple logistic regression. A total of 6298 patients were included. Mean age was 65.3±12.7 years, 75% were men, 27% had diabetes and 63% had hypertension. ST-elevation ACS was observed in 31% of patients. BMI ranged from 13.4 to 64.5kg/m²; 46% were overweight (25≤BMI<30) and 24% obese (BMI≥30). Weight ranged from 36 to 190kg. Mortality rate was 3.1% [95% CI:2.7%-3.5%]. Based on ROC curves, optimal cutoff points to predict in-hospital survival were 26kg/m² for BMI and 75kg for weight. In univariate logistic regression, BMI≥26kg/m² (OR=0.69; [95% CI]:0.52-0.92) or weight≥75kg (OR=0.57;[95% CI]:0.43-0.76) had a significant protective association with mortality. However, none of these associations remained significant in multivariate analysis. In EURHOBOP, higher BMI and weight in ACS patients were not associated with better short term in-hospital mortality.