Stroke is the second most common cause of death worldwide and is the complication of hypertension that is most directly linked to blood pressure. Hypertension affects nearly 30% of the world's population; therefore, reducing blood pressure is key for the prevention of stroke. Unlike the established role of hypertension as a risk factor for stroke, the prognostic importance of blood pressure in determining outcome after acute stroke is unclear. The acute hypertensive response occurs in more than 50% of all patients with acute stroke and is associated with poor prognosis. The relation between the outcome of acute stroke and blood pressure is U-shaped, with the best outcome at systolic blood-pressure levels ranging from about 140 to 180 mm Hg. The evidence that decreasing blood pressure in hypertensive patients with acute ischaemic or haemorrhagic stroke improves prognosis needs further confirmation. Whether raising blood pressure to improve perfusion of ischaemic brain areas is beneficial remains even more uncertain. Present guidelines for the management of blood pressure in patients with acute stroke are not evidence-based, but results from ongoing trials might provide more informed recommendations for the future.