Segmental arterial narrowing has rarely been angiographically demonstrated in patients with migraine. One new case is reported and 12 previous cases are reviewed. Though often referred to as vasospasm, arteriographic stenosis may result from edema of the vessel wall, arterial dissection, the effects of puerperium or arteritis. A biphasic course of spasm, similar to the pattern noted with subarachnoid hemorrhage, has been recorded in some migraineurs. The current neurogenic and biochemical concepts of "spasm" developed for subarachnoid hemorrhage are reviewed. Arterial narrowing may be important in several phenomena associated with migraine. It may account for migrainous cerebral infarction or hemorrhage. Vasoconstriction has also been invoked to explain the aura and other features of migraine. But the site of stenosis does not always correlate with the headache or focal neurologic features in location or timing. The angiographic changes are probably an epiphenomena rather than a primary mechanism of migraine. These changes may result from altered sympathetic neuronal activity; factors supporting that concept are reviewed.