To document the occurrence, time course, and predictors of global cognitive impairment following a supratentorial stroke, we prospectively studied 41 consecutive patients with acute cerebral ischemia and no evidence of pre-existing intellectual disturbances. The Graded Neurologic Scale and Mattis Dementia Rating Scale were used to assess neurologic and cognitive deficits within the first week, 3 weeks and 6 months after the onset of symptoms. CT was performed at each examination and semiquantitative measurements of infarct volumes and brain atrophy were obtained. Sixty-one percent of patients were found to be cognitively impaired within the first week. After 6 months this deficit had resolved in 24%, but was still present in 37% of individuals. Initial findings associated with a high risk of long-term intellectual dysfunction were: 1. moderately severe cognitive impairment, 2. diminished alertness in the acute stroke stage, 3. infarction involving the temporal lobe, 4. evidence of multiple brain infarcts and 5. pronounced ventricular enlargement. Logistic regression analysis revealed temporal infarcts and evidence of multiple ischemic lesions as the most powerful predictors of persistent cognitive impairment. By these two factors alone, 85.4% of study participants could be correctly classified regarding their cognitive outcome. These results suggest cognitive dysfunction to be a frequent sequela of supratentorial stroke. Its long-term persistence may be predicted on the basis of certain features.