Background; Increased level of N-Terminal Pro–B-Type Natriuretic Peptide (NT-proBNP) is known to be associated with adverse outcome in patients with acute coronary syndrome. We evaluated early outcomes of patients with acute myocardial infarction (AMI) according to the level of NT-proBNP as a substudy of KAMIR (Korean Acute Myocardial Infarction Registry). Method and Results; Study population consisted of 2253 patients (mean 64 years old, male 68.2%) who had baseline NT-proBNP level by electrochemiluminiscence immunoassay (ECLIA, NT-proBNP kit, Roche Diagnostics, Mannheim, Germany). The highest quartile group demonstrated a significantly lower left ventricular ejection fraction than the other quartiles (quartile 1=55.3짹11.3%, quartile 2=54.8짹11.01%, quartile 3=51.4짹11.2%, and quartile 4=44.3짹12.6%, P<.001). In-hospital mortality rate was increased according to the higher quartile group (quartile 1= 0.5% ; quartile 2=1.4% , quartile 3=2.0%; quartile 4=8.3% , P<.001). Increased quartiles are also associated with the increased major cardiovascular adverse event (cardiac and noncardiac death, MI, revascularization, and coronary artery bypass surgery) rates at 1 month follow up (quartile 1 =0.7% ; quartile 2=1.0% ; quartile 3=1.9% ; quartile 4= 7.4% , P<.001). Conclusions: Increased baseline level of NT-proBNP is associated with adverse in-hospital mortality and MACE rate at 1 month follow-up. This study suggests that baseline NT-proBNP level can be used as a short-term prognostic factor in patients with AMI.