Background and Objectives: B-type natriuretic peptide (BNP) reflects ventricular impairment, the severity of hemodynamic decompensation, and also associated with prognosis in patients with acute coronary syndromes. The aim of this study was to evaluate the role of BNP as a prognostic marker of adverse cardiac events or left ventricular (LV) dysfunction in patients with acute myocardial infarction (AMI). Methods: From January 2004 to January 2005, 139 patients (61.4짹11.5 years old; 112 males) with AMI who measured BNP were enrolled. In-hospital events including death, cardiogenic shock, respiratory failure needing mechanical ventilation, or re-infarction and major adverse cardiac events (MACE) during clinical follow-up were analyzed. Echocardiographic parameters of LV function were also analyzed. Results: Mean BNP level on admission was 2161.6짹3289.4 pg/ml and higher in anterior wall infarction than in other infarctions (3041.9짹4206.9 vs 1387.7짹1881.2 pg/ml, p=0.009). BNP level showed significant negative correlation with LV ejection fraction (EF) (r=-0.35) and positive correlation with total wall motion score (r=0.31) and peak C-reactive protein level (r=0.45). Eighteen patients (12.9%) had in-hospital events (3 death, 10 cardiogenic shock, 4 mechanical ventilation, 1 recurrent MI). Mean BNP level was significantly higher in patients with in-hospital events than in patients without in-hospital events (5409.1짹4914.5 vs 1550.1짹2439.4 pg/ml, p=0.003). Optimal cut-off value of the BNP level for predicting in-hospital events using receiver operating characteristic curve was 2477 pg/ml (sensitivity: 70%, specificity: 86%). Mean BNP level showed significant negative correlation with follow-up LV EF (r=-0.38). Conclusion: Mean BNP level on admission was a useful prognostic marker for predicting in-hospital events and LV dysfunction in patients with AMI.