Background Acute myocardial infarction is known as an acute metabolic stress, but clinicians currently have limited guidance regarding the evaluation and management of hyperglycemia after revascularization. Methods and results We assessed the prognostic role of three different ranges of in-hospital peak glycemia (<140, 140–180, and >180 mg/dl) in 252 acute ST-segment elevation myocardial infarction patients without earlier known diabetes submitted to percutaneous coronary intervention consecutively admitted to our intensive cardiac care unit (ICCU). Patients with highest peak glycemia showed the highest intra-ICCU mortality (7/44, 15.9%), which was significantly higher with respect to the other two subgroups ( P=0.001 and 0.034, respectively). At backward stepwise logistic regression analysis, peak glycemia (odds ratio: 3.14; 95% confidence interval: 1.01–9.74, P=0.047) was an independent predictor of intra-ICCU mortality. Conclusion In acute ST-segment elevation myocardial infarction patients without earlier known diabetes submitted to mechanical revascularization, the poorer in-hospital glucose control was associated with higher mortality; peak glycemia greater than 180 mg/dl was associated with the highest mortality, whereas patients with peak glycemia comprised between 140 and 180 mg/dl exhibited intermediate mortality rates. According to our data during hospitalization intensivists should achieve glucose control values less than 140 mg/dl, as peak glycemia resulted in the independent predictor of intra-ICCU mortality.