Background: ST-segment elevation myocardial infarct (STEMI) is one of the most common life threatening diseases. The incidence and predictors of in-hospital mortality has only limited data in Korean. So, we evaluated the incidence and predictors of in-hospital mortality in patients with STEMI. Methods: Total 658 patients with STEMI who underwent percutaneous coronary intervention (PCI) from May 2003 to Dec. 2008 were included. All subjects were divided into two groups according to the in-hospital mortality. Results: 37 (5.6%) of 658 patients died before discharge. 31 of 37 patients died due to myocardial infarct related heart failure and the others due to bleeding. There was no difference in sex. Patients with mortality was older (60.9 짹 12.2 vs 69.3 짹 11.8, p < 0.01) and had history (Hx) of previous myocardial infarct (MI) and previous PCI (previous MI: 6.9% vs 18.9%, p < 0.01; previous PCI: 7.6% vs 18.9%, p = 0.15). There was no difference of Hx of hypertension, diabetes, chronic renal failure. Higher killip class and multi-vessel disease (MVD) were seen in mortality group (killip 4: 11.9% vs 64.9%, p < 0.01; 3-vessel disease: 17.1% vs 54.1%, p < 0.01). Higher incidence of left main (LM) disease was seen in mortality group (LAD: 50.8% vs 56.3%; LCX: 10.9% vs 6.3%, RCA 38.1% vs 28.1%, LM: 0.2% vs 9.4%, p < 0.01). Mortality groups showed frequent tachy- or bradyarrhtymia. (tachyarrhythmia: 6.8% vs 20.7%; bradyarrhythmia: 7.8% vs 20.7%; p < 0.01). Most of patient with mortality underwent primary PCI (54.3% vs 83.8%, p < 0.01). Femoral artery approach was frequently used in mortality group (45.4% vs 66.7%, p < 0.01). There was no difference in initial TIMI flow grade. Lower total cholesterol level but higher initial BNP level were seen in mortality group (Total cholesterol, mg/dl: 178.7 짹 42.4 134.5 짹 67.3, p = 0.02; BNP, pg/ml: 116.2 짹 305.6 vs 364.3 짹 613.1, p = 0.019). There was no difference in peak cardiac enzyme level. Logistic regression analysis revealed that age, killip class and LM disease were independent predictors of in-hospital mortality (Age: odds ratio(OR) = 1.06, 95% confidence interval(CI) = 1.011~1.108, p < 0.05; Killip class: OR = 2.63, 95% CI = 1.898-3.688, p < 0.01; LM: OR = 5.69, 95% CI = 1.950~16.592, p < 0.04). There was no difference of initial ejection fraction (EF) due to limited data in mortality group. Conclusion: The incidence of in-hospital mortality in patients with STEMI who underwent PCI was about 6%. The independent predictors of in-hospital mortality were age, higher killip class and left main disease.