BACKGROUND: The long-term outcomes of diabetic patients presenting with ST-segment elevation myocardial infarction (STEMI) in contemporary practice have received limited study. METHODS: We evaluated the clinical characteristics and outcomes of STEMI patients with and without diabetes in a large regional STEMI program designed to facilitate timely primary percutaneous coronary intervention (PCI) (Minneapolis Heart Institute at Abbott Northwestern Hospital, Minneapolis, MN). The primary and secondary outcome measures were in-hospital mortality, 1-year major adverse cardiovascular events (MACE) (stroke, myocardial infarction, unplanned PCI or coronary artery bypass graft [CABG] surgery, and all-cause mortality), and 5-year mortality. RESULTS: Of the 6292 patients included, 1158 (18.4%) had Diabetes Mellitus (DM) (95.3% Type II, 4.7% Type I). Patients with DM were older (mean age 66 vs. 62.8 years, p < 0.01), had more co-morbidities and were more likely to receive medical therapy without reperfusion (13% vs. 10%, p = 0.003). Patients with DM had higher in-hospital (8% vs. 5%, p = 0.001), 1-year (8% vs. 4%, p < 0.001) and 5-year mortality (16% vs. 9%, p < 0.001) compared to non-diabetics. On Cox proportional hazards analysis, DM was independently associated with worse mortality (hazard ratio: 1.70, 95% confidence interval (CI): 1.32-2.19, p < 0.001) and MACE [HR: 1.63 (95% (CI)): 1.28-2.08, p < 0.001]. CONCLUSIONS: Despite advancements in medical therapy and revascularization strategies for STEMI, DM remains independently associated with higher short- and long-term morbidity and mortality in contemporary practice.