BACKGROUND: Hyperglycemia can increase the risk of death or a poor outcome following acute myocardial infarction (AMI). METHODS: From Nov 2005 to Dec 2006, the study population comprised of 627 consecutive patients admitted with AMI within 24 hours of the start of symptoms. The final diagnosis was non-ST elevation myocardial infarction (NSTEMI) in 29.7% (186/627) and ST elevation myocardial infarction (STEMI) in 70.3% (441/627). The groups were divided according to glucose level of admission; Group I was below 96 mg/dL (38/627, 6.1%), Group II was between 97 and 110 mg/dL (60/627, 9.6%), Group III was between 111 and 125 mg/dL (72/627, 11.5 %) and Group IV was above 126 mg/dL (457/627, 72.9 %). We compared groups with the risk factor, severity, comorbidity and 6 months follow-up survival rate. RESULTS: During follow-up 6 months, 21 (3.3 %) patients died. The male was more predominant as increasing glucose level [male/total = 456/627 (72.7%), 32/38 (84.2%) in Group I; 44/60 (73.3%) in Group II; 58/72 (80.6%) in Group III; 322/457 (70.5%) in Group IV] (p=0.052). The severity of myocardial infarction was significantly increased as glucose level of admission [Killip III/IV/total = 72/627 (11.5%), 4/38 (10.5%) in Group I; 2/60 (3.3%) in Group II; 5/72 (6.9%) in Group III; 61/457 (13.3%) in Group IV] (p=0.005). There were considerable differences between groups in the comorbidity of hypertension [13/38 (34.2%) in Group I; 24/60 (40.0%) in Group II; 30/72 (41.7%) in Group III; 227/457 (49.7%) in Group IV] (p=0.018) and diabetes mellitus [4/38 (10.5%) in Group I; 2/60 (3.3%) in Group II; 4/72 (5.6%) in Group III; 170/457 (28.7%) in Group IV] (p=0.0001). The incidence of STEMI was more increased as glucose level of admission [18/38 (47.4%) in Group I; 34/60 (56.7%) in Group II; 51/72 (70.8%) in Group III; 338/457 (70.3%) in Group IV] (p=0.0001). There were no differences between groups in the smoking, age, hyperlipidemia and 6-month survival rate. CONCLUSIONS: In patients with AMI, hyperglycemia at admission was associated with increased severity of myocardial infarction, comorbidity of hypertension and diabetes mellitus, and displayed more predominance of male and STEMI.