TIA is usually caused by embolism from a carotid stenosis. The stenosis has no hemodynamic significance, but recent studies of regional cerebral blood flow have indicated that this occurs in a few cases. Traditionally, TIA are not considered to cause cerebral damage, but CT-studies have revealed a number of silent infarcts and rCBF measurements have shown even more persistent abnormalities of blood flow. In classic migraine, alterations of rCBF are completely different, indicating a mechanism progressing in the cerebral cortex, probably the spreading depression of Leao. Similar blood flow changes are not seen in common migraine, where tomographic rCBF determinations have been normal.