The frequency of cerebral vascular accidents justifies a rapid evaluation of the patients to distinguish between ischaemia and haematoma. In acute cerebral ischaemia, data from the literature show that magnetic resonance imaging is sensitive early (4th to 6th hours) and anatomically efficient (posterior fossa, brain stem) although it lacks specificity, being based on water movements alone. The most difficult differential diagnosis in the acute phase is bleeding, and in that phase early computerized tomography images are easier to interpret.