This paper reviews current evidence on the role of admission and fasting glycaemia as prognostic markers in patients with acute coronary syndromes. Though both parameters are correlated, they give different prognostic information and are related to both in-hospital complications, including death, and long-term outcomes. As hyperglycemia at the acute stage of myocardial infarction is an independent predictor of untoward cardiovascular events, blood glucose measurements should become routine in all patients presenting with acute coronary syndromes.