BACKGROUND: There are limited data describing the presenting characteristics, management, and outcomes of diabetic and nondiabetic patients with an acute coronary syndrome (ACS). OBJECTIVE: To examine differences in these factors, patients with ST-segment elevation acute myocardial infarction, non-ST-segment elevation acute myocardial infarction, and unstable angina were enrolled in a large multinational coronary disease registry. METHODS: The Global Registry of Acute Coronary Events is a prospective observational study of patients hospitalized with an ACS at 94 hospitals in 14 countries. The study sample consisted of 5403 patients with ST-segment elevation acute myocardial infarction, 4725 with non-ST-segment elevation acute myocardial infarction, and 5988 with unstable angina. RESULTS: Approximately 1 in 4 patients presented to participating hospitals with a history of diabetes. Patients with diabetes were older, more often women, with a greater prevalence of comorbidities, and they were less likely to be treated with effective cardiac therapies than nondiabetic patients. Patients with diabetes who developed an ACS were at increased risk for each hospital outcome examined including heart failure, renal failure, cardiogenic shock, and death. These differences remained after adjustment for potentially confounding prognostic factors. CONCLUSIONS: A considerable proportion of patients with an ACS has diabetes and is at increased risk for adverse outcomes compared with patients without diabetes. There are certain proven therapeutic strategies that remain underused in the diabetic population. A more widespread awareness of this increased risk and a more diligent use of proven cardiac treatment approaches are indicated for patients with diabetes who develop an ACS.