This study compared the prognosis of ST-elevation myocardial infarction (STEMI) in patients with multivessel disease (MVD) with that of single vessel disease (SVD) and investigated the revascularization benefit of noninfarct-related artery (IRA) in MVD patients undergoing primary percutaneous coronary intervention (PCI). Between 2002 and 2009, 1278 patients with STEMI underwent primary PCI. Of these patients, 717 (56.1%) with SVD (only IRA obstruction) were placed in group A, while 561 (43.9%) with MVD (Group B) were further categorized into group 1 (PCI for IRA) and group 2 (staged PCI for IRA+non-IRA). The results demonstrated a lower degree of successful reperfusion in IRA and higher 30-day and 1-year cumulative mortality rates in group B (P < 0.001). While there was no difference in successful reperfusion in IRA between group 1 and group 2, the 30-day and one-year cumulative mortality rates were higher in group 1. Multivariate analysis identified MVD as an independent predictor of 1-year mortality (P < 0.001). In conclusion, patients with subsequent PCI for MVD had better 30-day and 1-year outcomes than those with conservative treatment.