The objective of this study was to determine short- and long-term cardiovascular outcomes in unselected patients with diabetes mellitus (DM) with acute ischemic chest pain (AICP). In patients with DM presenting to the emergency department with AICP, short-term cardiovascular outcomes remain discordant between trials and registries, whereas long-term outcomes are not well-described. A consecutive cohort of all residents of Olmsted County, Minnesota, presenting with AICP from January 1, 1985, to December 31, 1992, was followed for a median duration of 16.6 years. The primary outcome was long-term all-cause mortality. Other outcomes included a composite of death, myocardial infarction, stroke, and revascularization (major adverse cardiovascular and cerebrovascular events [MACCEs]) as well as heart failure (HF) events at 30 days and at a median of 7.3 years, respectively. Of the 2,271 eligible patients, 336 (14.8%) were classified with DM. The crude 30-day MACCE rate was 10.1% in patients with DM and 6.1% in those without DM (p = 0.007). HF events were more common in patients with DM at 30 days (9.8% vs 3.1%, p <0.001). At 7.3 years, patients with DM were more likely to experience MACCEs and HF events than those without DM (71.2% vs 45.1%, unadjusted hazard ratio 2.15%, 95% confidence interval 1.87 to 2.48, p <0.001, and 45.1% vs 18.2%, p <0.001, respectively). Over the follow-up period, 272 patients with DM (81.9%) died, compared with 936 (49.2%) without DM (p <0.001). In conclusion, DM is associated with a higher short-term risk for MACCEs and HF and a higher long-term risk for mortality in unselected patients with AICP. DM should be included as a high-risk variable in national acute coronary syndrome guidelines.