Elevated blood glucose and its potential link with adverse outcomes in patients with acute myocardial infarction (AMI) has been the subject of intense study over more than 40 years. The numerous observational studies performed to date have addressed some of the questions in this field, but many critically important questions are still poorly understood, and remain subjects of debate. This review summarises current epidemiological data on the prevalence of hyperglycaemia in the AMI patient population and its relationship to patient outcomes, and addresses some of the existing controversies in the field.