Hyperglycaemia is present in 40-60% of patients with acute ischaemic stroke and adversely affects survival and outcome. This effect is independent of stroke severity or pathology, and is most striking in patients without recognised diabetes, in whom the odds of death are increased threefold, and the chance of poor functional outcome by 40%. Hyperglycaemia remains a powerful independent predictor of outcome even in the face of thrombolytic drug therapy.