To assess the impact of hyperglycemia in different age-groups of patients with acute myocardial infarction (AMI). A total of 2,027 patients with AMI were categorized into one of five age-groups: <50 years (n = 301), ≥50 and <60 (n = 477), ≥60 and <70 (n = 545), ≥70 and <80 (n = 495), and ≥80 years (n = 209). Hyperglycemia was defined as initial glucose ≥115 mg/dL. The adjusted odds ratios for hyperglycemia predicting hospital mortality in groups 1-5 were, respectively, 7.57 (P = 0.004), 3.21 (P = 0.046), 3.50 (P = 0.003), 3.20 (P < 0.001), and 2.16 (P = 0.021). The adjusted P values for correlation between glucose level (as a continuous variable) and mortality were 0.007, <0.001, 0.043, <0.001, and 0.064. The areas under the ROC curves (AUCs) were 0.785, 0.709, 0.657, 0.648, and 0.613. The AUC in group 1 was significantly higher than those in groups 3-5. The impact of hyperglycemia as a risk factor for hospital mortality in AMI is more pronounced in younger patients.