The aim was to evaluate management and outcomes in patients with diabetes mellitus (DM) with acute coronary syndrome (ACS). The EHS-ACS-II was a multinational survey conducted in 2004 that included 6,385 consecutive patients with ACS. The management and outcomes of patients with and without DM were compared. DM was recognized in 1,587 patients (25%) with ACS. Patients with DM had a less favorable risk-factor profile, less typical presentation, and longer delay in seeking medical attention; presented more frequently with arrhythmias, heart failure, renal failure, and major bleeding; and had higher in-hospital and 1-year mortality. They were treated more often with diuretics and inotropic agents and less often with antiaggregants (glycoprotein IIb/IIIa and clopidogrel). Insulin was administered to 53% of patients with DM during hospitalization and 31% at discharge. Patients with DM with ST-elevation (STE) myocardial infarction underwent similar primary percutaneous and coronary interventions (but received less thrombolytic therapy). Patients with DM with non-STE ACS underwent less in-hospital revascularization and had significantly higher 1-year mortality. Multivariable analyses showed DM as a predictor of 1-year mortality (odds ratio 1.37, 95% confidence interval 1.09 to 1.71), but not in-hospital mortality. In conclusion, given the current treatment, patients with and without DM with ACS had similar in-hospital adjusted mortality, but patients with DM had increased 1-year mortality. Patients with DM with non-STE ACS posed a higher risk group.