Background: It has been suggested that admission glucose in patients with acute myocardial infarction (AMI) is associated with increased in-hospital mortality and poor clinical outcome regardless of the presence of diabetes. We sought to assess relationship of admission glucose to early and late clinical outcome in Korean patients with AMI Methods: Among 25,559 patients with acute MI enrolled in the Korea Acute Myocardial Infarction Registry and Korea Working Group on Myocardial Infarction Registry between November 2005 and July 2010, a total of 13,331 patients followed up for 1 year were analyzed. Patients with a history of diabetes or those newly diagnosed with diabetes at admission were excluded. Patients were divided into three groups according to glucose level at admission: group I (<140 mg/dL, n=7,604, 65.5짹13.5 years, female 24.8%), group II (140~200 mg/dL, n=4,318, 66.9짹13.1 years, female 28.4%), and group III (>200 mg/dL, n=1,409, 69.8짹13.1 years, female 36.4%). In-hospital and 1-year clinical outcome were compared among three groups. Results: Compared to group I and II, group III had more often acute ST-elevation MI, atypical chest pain at presentation, left main disease, lesion type C, pre-procedural Thrombolysis In Myocardial Infarction flow grade 0, and left ventricular ejection fraction<40%. During hospitalization, patients in group III had higher mortality and were more likely to suffer cardiogenic shock, ventricular arrhythmia, atrial fibrillation, new heart failure and advanced atrioventricular block. One-year mortality increased with increasing admission glucose levels: 389 (5.6%) vs. 351 (8.9%) vs. 326 (25.3%) patients in group I, II, and III, respectively (p=0.001). Adjusted Cox regression analysis also showed higher 1-year mortality in group II than in group I (hazard ration [HR], 1.40; 95% confidence interval [CI], 1.20-1.63; p=0.001), in group III than in group I (HR, 3.20; 95% CI, 2.73-3.76; p=0.001), and in group III than in group II (HR, 2.32; 95% CI, 1.97-2.72; p=0.001). Conclusions: Higher level of admission glucose in patients with AMI was associated with higher in-hospital and 1-year mortality.