Some patients with cerebral arteriovenous malformations (AVMs) suffer recurrent migrainous attacks which meet the official criteria for migraine. The relationship of these attacks to the malformations has been poorly substantiated. Instances where attacks disappeared following surgical extirpation of an AVM support a relationship, but several other reported surgical outcomes do not. Both patients presented here had surgical results seemingly antithetical to a relationship: the attacks persisted in the first patient and began in the second after removal of the AVM. Nevertheless, data assembled from the literature attests to a causal role for AVMs in the production of migrainous attacks, by showing an overwhelming correlation between the side of the cranium with the AVM and the side afflicted by unilateral headache. An equally good correlation exists for lateralized auras. The correlative and surgical data together show that migrainous attacks develop in relation to AVMs, but not within the malformation itself. Instead, the neighboring brain is probably the generative site.