Aim: The aim of the present study was to assess the prognostic implications of admission hyperglycemia in non-diabetic acute myocardial infarction patients. Methods: The present observational enrolled consecutive NSTE-ACS patients treated at the Department of Cardiology for the period of 2 years. A total of 250 patients with NSTE-ACS and high BG without history of diabetes were enrolled. Results: Age, sex, hypertension, hyperlipidaemia, smoking, and history of myocardial infarction (p > 0:05 for all) did not significantly differ among the three groups. The rates of multivessel disease, renal insufficiency, Killip grade III/IV, and emergency PCI, as well as the levels of high-sensitivity C-creatine kinase isoenzyme MB (CK-MB) (p < 0:05 for all), differed significantly across the three groups, however. Significantly more deaths, malignant arrhythmias, and severe pump failures occurred in groups B and C than in group A (p < 0:05). Group C had a greater incidence of malignant arrhythmia, severe pump failure, and mortality (p < 0:05) in comparison to group B.Logistic regression analysis was performed with in-hospital death as the dependent variable and the previously identified risk factors as independent variables. The results showed that hyperglycemia, age, renal insufficiency, and severe pump failure were risk factors of in-hospital death. Conclusion: In individuals with undiagnosed diabetes as opposed to those with established diabetes, hyperglycemia is a stronger predictor of adverse outcomes. Those who have never had diabetes treatment and are undiagnosed as diabetics may be more vulnerable, particularly if they have significant hyperglycemia.