The aim of this study was to describe differences in the characteristics and short- and long-term prognoses of patients with first acute myocardial infarction (MI) according to the presence of ST-segment elevation or nonST-segment elevation. From 2001 and 2003, 2,048 patients with first MI were consecutively admitted to 6 participating Spanish hospitals and categorized as having ST-segment elevation MI (STEMI), nonST-segment elevation MI (NSTEMI), or unclassified MI (pacemaker or left bundle branch block) according to electrocardiographic results at admission. The proportions of female gender, hypercholesterolemia, hypertension, and diabetes were higher among NSTEMI patients than in the STEMI group. NSTEMI 28-day case fatality was lower (2.99% vs 5.26%, p = 0.02). On multivariate analysis, the odds ratio of 28-day case fatality was 2.23 for STEMI patients compared to NSTEMI patients (95% confidence interval 1.29 to 3.83, p = 0.004). The multivariate adjusted 7-year mortality for 28-day survivors was higher in NSTEMI than in STEMI patients (hazard ratio 1.31, 95% confidence interval 1.02 to 1.68, p = 0.035). However, patients with unclassified MI presented the highest short- and long-term mortality (11.8% and 35.4%, respectively). The excess of short-term mortality in unclassified and STEMI patients was mainly observed in those patients not treated with revascularization procedures. In conclusion, patients with first NSTEMI were older and showed a higher proportion of previous coronary risk factors than STEMI patients. NSTEMI patients had lower 28-day case fatality but a worse 7-year mortality rate than STEMI patients. Unclassified MI presented the worst short- and long-term prognosis. These results support the invasive management of patients with acute coronary syndromes to reduce short-term case fatality. © 2011 Elsevier Inc.