Background: Stent thrombosis (ST) is one of the most devastating complications after percutaneous coronary intervention (PCI), although it is rare. We aimed to assess incidence, outcomes and predictors of ST in Korean patients with acute myocardial infarction (AMI). Methods: A total of 3,838 eligible patients from Korea Acute Myocardial Infarction Registry (KAMIR) study (63.3짹12.8 years, 69.6% men) undergoing PCI were retrospectively analyzed. They were divided into two groups according to presence of angiographic ST (ST group: n=51, non-ST group: n=3787). ST was defined according to ARC definition as acute (< 24 hours), subacute (24 hours to 30 days), late (>30 days to 1 year), or very late (>1 year) ST. Results: The incidence of ST was 1.3% in KAMIR. Patients in ST group were younger than those in non-ST group (58.6짹11.9 vs. 63.4짹12.8 years, p=0.009). ST group tended to have more men (82.0% vs. 69.6%, p=0.057), but less diabetic patients (16.3% vs. 28.7%, p=0.058). ST-segment elevation myocardial infarction (STEMI) was diagnosed more in ST group (76.0% vs. 60.0%, p=0.021). There were 46 DES (91.8%) and 5 bare metal stent (BMS) implantations (8.2%) in ST group. No significant differences were noted according to type of drug-eluting stent (DES). Stent length and diameter were not significantly different between groups, but the number of stents was greater in ST group (1.8짹0.9 vs. 1.5짹0.8, p=0.014). Thrombolysis in Myocardial Infarction (TIMI) flow before PCI was significantly worse in ST group (TIMI 0: 62.5% vs. 47.7%, p=0.042). There were no differences in aspirin or clopidogrel use between both groups but cilostazol was tended to be prescribed more in ST group (39.6% vs. 27.0%, p=0.052). At 1 year follow-up, death and myocardial infarction were greater in ST group (28.6% vs. 13.6%, p=0.005). Also, target lesion revascularization (50.0% vs. 18.3%, p=0.008) and target vessel revascularization rate (64.3% vs. 24.2%, p=0.002) were higher in ST group. In multivariable logistic regression analysis, the number of stents (OR 1.51, 95% CI 1.09-2.10, p=0.013), pre-TIMI flow 0 (OR 2.42, 95% CI 1.13-5.18, p=0.023) and low left ventricular ejection fraction (OR 2.44, 95% CI 1.01-5.64, p=0.036) were independent predictors for ST. Conclusion: Multiple stent use in totally occluded coronary artery in patients with left ventricular dysfunction might be associated with ST. Since patients with ST showed worse long-term outcomes, high risk patients may have to receive more intensive anti-thrombotic therapy.