OBJECTIVE This study aimed to compare mortality rates after discharge between the patients with non-ST-elevation myocardial infarction (NSTEMI) and those with ST-elevation myocardial infarction (STEMI), and identify each mortality risk factors in these two types of myocardial infarction. METHODS Between 2011 and 2015, 13105 consecutive patients were enrolled in the Korea Acute Myocardial Infarction-National Institute of Health registry (KAMIR-NIH); 12271 patients with acute myocardial infarction met the inclusion criteria and were further stratified into the STEMI (n=5828) and NSTEMI (n=6443) groups. The occurrence of mortality and cardiac mortality at 3 years were compared between groups, and the factors associated with mortality for NSTEMI and STEMI were evaluated. RESULTS The comparison between these two groups and long-term follow-up outcomes showed that the cumulative rates of all-cause and cardiac mortality were higher in the NSTEMI group than in the STEMI group [all-cause mortality: 10.9% vs. 5.8%; hazards ratio (HR), 0.464; 95% confidence interval (CI), 0.359-0.600, p<0.001; cardiac mortality: 6.6% vs. 3.5%, HR, 0.474; 95% CI, 0.344-0.654, p<0.001, respectively). In the NSTEMI group, low left ventricular ejection fraction (LVEF; <40%), no percutaneous coronary intervention (PCI), old age (≥65 years), and low hemoglobin level (<12 g/dL) were identified as risk factors for 3-year mortality. In the STEMI group, old age, low glomerular filtration rate (<60 mL/min/1.73 m²), low LVEF, high heart rate (>100 beats/min), no PCI, and low hemoglobin level were identified as the risk factors for 3-year mortality. CONCLUSIONS The NSTEMI group had higher mortality compared to the STEMI group during the 3-year clinical follow-up after discharge. Low LVEF and no PCI were the main risk factors for mortality in the NSTEMI group. In contrast, old age and renal dysfunction were the risk factors for long-term mortality in the STEMI group.