Twenty-two patients with acute migraine-associated stroke were prospectively evaluated; 91% were female, and 23% had a prior history of presumed migrainous stroke. The incidences of major stroke risk factors and mitral valve prolapse were no higher for the study group than for the general population of similar age. Computed tomography, magnetic resonance imaging, or radionucleotide scanning of the brain was performed on all patients, and demonstrated ischemic or hemorrhagic infarction in 12 (55%). Cerebral arteriography revealed abnormalities related to the acute stroke in five (42%) of 12 cases overall, and in four (67%) of six studies performed within 72 hours of stroke onset; one patient (8%) suffered significant complications from arteriography. Although a variety of processes, alone or in combination, may contribute to migrainous stroke, extracranial and/or intracranial vasospasm appears to play a major role in at least some cases.