Background: N-Terminal Pro–B-Type Natriuretic Peptide (NT-proBNP) is associated with an adverse short-term outcomes in patients with ST-elevated myocardial infarction (STEMI). We evaluated long-term outcomes in patients with STEMI according to NT-proBNP level as a substudy of Korean Working Group on Myocardial Infarction (KorMI). Method: Study population consisted of 1121 consecutive patients (mean 62.4짹13.0 years old, male 75.0%) with STEMI of onset ��� 12 hours who underwent primary Percutaneous coronary intervention (PCI) and who had baseline NT-proBNP level by electrochemiluminiscence immunoassay (ECLIA, NT-proBNP kit, Roche Diagnostics, Mannheim, Germany). Study subjects were divided by quintile group according to NT-proBNP level. Results: The highest quintile group had older age (quintile 1=53.5짹9.8yr; quintile 2=60.3짹11.6yr; quintile 3=63.5짹12.7yr; quintile 4=63.5짹13.2yr; quintile 5=71.0짹11.1yr, p<0.001) and lower left ventricular ejection fraction than other quintile groups (quintile 1=54.3짹9.5%; quintile 2=53.6짹10.1%; quintile 3=52.9짹11.6%; quintile 4=52.0짹10.9%; quintile 5=46.1짹11.5%, p<0.001). In-hospital mortality rate was increased according to the higher quintile group (quintile 1=1.3%; quintile 2=2.2 %; quintile 3=0.4 %; quintile 4=2.7%; quintile 5=6.7% , P<.001). Increased quartiles are also related with the increased major adverse cardiovascular event (cardiac and noncardiac death, myocardial infarction and revascularization) rates at 6 month follow up (quintile 1=2.6%; quintile 2=1.8%; quintile 3=4.0%; quintile 4= 6.8 %; quintile 5=9.1, P=.043). Conclusion: Increased baseline level of NT-proBNP is related with MACE rate at 6 month follow-up. This study suggests that baseline NT-proBNP level can be used as a long-term prognostic factor in patients with STEMI underwent primary PCI.