INTRODUCTION: Diabetes Mellitus is known to be a major risk factor for cardiovascular disease. Patients (Diabetic, non diabetic), during the onset of an acute myocardial infarction, tend to have increased blood glucose concentration (blood glucose concentration > 200 mg%). AIM: The aim of our study was to asses the prognostic value of increased blood glucose at the onset of an acute myocardial infarction (AMI). METHODS: We enrolled 674 patients (506 male - 168 female, mean age 64.58 +/- 12.38 years) with AMI in a 3 year period. Patients were recruited according to their blood glucose during administration in the coronary care unit and the history of Diabetes Mellitus. Epidemiological, biochemical and clinical data were examined, also mortality, and complications, during their hospitalization and for 12 month follow up period. RESULTS: Hyperglycemia was an independent mortality risk factor during the 12 months follow up (16.32% to 7.12% p=0.03 - OR=4.9) and had a strong correlation with cardiogenic shock (p=0.04 - OR=2.83). In non diabetic patients (n=441, 348 male - 93 female, mean age 62.21 +/- 12.96) hyperglycemia was found in 84 patients (19.05%, group 13). The other 357 patient had blood glucose concentration below 200mg% (80.95% group A). The group B had significantly increased mortality rate during the 12 months follow up (11.9% to 5.95% p=0.043 - OR=1.19). In diabetic patients (n=233, 155 male - 78 female, mean age 68.97 +/- 9.7) hyperglycemia was found in 185 patients (79.4% group C) and the rest 48 (20.6%) had blood glucose concentration within the limits (group D). The group C had significantly increased mortality rate during the 12 months follow up (17.84% to 6.25% p=0.03 - OR=3.97). CONCLUSION: Hyperglycemia has been shown to be associated with worse short and long-term survival after acute myocardial infarction. Our study demonstrates the benefit of a well controlled diabetic patient during the onset of myocardial infarction and the intimate need for proper and effective primary diagnose of diabetes mellitus.