Objective We aimed to describe current characteristics of patients admitted for acute coronary syndrome (ACS) in Western Europe and to analyse whether international in-hospital mortality variations are explained by differences in patients’ baseline characteristics and in clinical management. Methods We studied a population-based longitudinal cohort conducted in Finland, France, Germany, Greece, Portugal and Spain, and comprising 12 231 consecutive ACS patients admitted in 53 hospitals between 2008 and 2010. Baseline characteristics, clinical management and inhospital outcomes were recorded. Contextual effect of country on death was analysed through multilevel analysis. Results Of all patients included, 8221 (67.2%) had NSTEMI (non-ST-elevation myocardial infarction), and 4010 (32.8%) had STEMI (ST-elevation myocardial infarction). Inhospital mortality ranged from 15.1% to 4.9% for German and Spanish STEMI patients, and from 6.8% to 1.9% for Finnish and French NSTEMI patients (p<0.001 for both). These international variations were explained by differences in patients’ baseline characteristics (older patients more likely to have cardiogenic shock in Germany) and in clinical management, with differences in rates of thrombolysis (less performed in Germany) and primary percutaneous coronary intervention (high in Germany, low in Greece). A remaining contextual effect of country was identified after extensive adjustment. Conclusions Inhospital mortality rates of STEMI and NSTEMI patients were two to three times higher in Finland, Germany and Portugal than in Greece and Spain, with intermediate values for France. Differences in baseline characteristics and clinical management partly explain differences in outcome. Our data also suggest an impact of the healthcare system organisation.