Backgrounds: It has been suggested that admission hyperglycemia is associated with poor outcomes in patients with acute myocardial infarction (AMI). The aim of this study was to assess the relationship between admission hyperglycemia and long-term prognosis in patients with AMI. Methods: A total of 6,030 AMI patients without a previous history of diabetes were enrolled between Nov. 2005 and Jan. 2008. The patients were divided into three groups according to admission serum glucose levels: group I (<140 mg/dL, n=3,307), group II (140-200 mg/dL, n=1,946), and group III (>200mg/dL, n=777). In-hospital and one-year mortality were compared between the groups. Results: The mean age was 64.0, 65.7, and 67.4 years in group I, II, and III, respectively. The proportion of female gender (23.9%, 29.5%, 35.0%; p<0.001), Killip class IV (2.8%, 5.5%, 14.0%; p<0.001), ST-segment elevation myocardial infarction (54.6%, 71.5%, 71.7%; p<0.001), and in-hospital mortality (3.5%, 7.5%, 19.7%; p<0.001) progressively increased with higher tertiles of elevated values of initial serum glucose. No significant differences existed among the three groups in the success rate of percutaneous coronary intervention and in the prevalence of hypertension, smoking, and hyperlipidemia. Compared with group I, odds ratio (OR) for mortality rate were significantly increased in group II [OR 1.32, 95% confidential interval (CI) 1.09-1.60, p=0.004)], and in group III (OR 1.63, 95% CI 1.34-1.98, p<0.001), compared with group I. And also significant differences were existed between group II and group III (OR 1.23, 95% CI 1.01-1.49, p=0.04). Conclusion: Admission glucose in patients with AMI provides incremental prognostic value and significantly correlates with in-hospital and one-year mortality.