Stress hyperglycaemia is a common event in acute critical illness. There is increasing evidence that maintaining normoglycaemia and treatment with insulin (or with glucose-insulin-potassium [GIK]), even in non-diabetic persons, is helpful in limiting organ damage after myocardial infarction, stroke, traumatic brain injury and other conditions, even though the conditions may be accompanied by insulin resistance. A landmark study now suggests that maintaining normoglycaemia with intensive insulin treatment in a heterogeneous population of critically ill patients decreases morbidity and mortality. The potential mechanisms that underlie such a beneficial effect are discussed.