Migraine is a common condition with, usually, stereotyped symptomatology, suggesting that it is a specific disease entity (a morbus sui generis). However, occasionally a migraine sufferer will exhibit atypical manifestations of the condition; also, some specific diseases such as systemic lupus erythematosus and arteriovenous malformations, may exactly mimic the symptoms of migraine. These latter considerations raise the possibility that migraine is a syndrome rather than a disease. The recent delineation of the trigeminovascular system allows a conception of migraine as being neither disease nor syndrome, but rather a constitutional predisposition of the neurovascular system to react excessively to internal or external stimuli by a pattern of hyperactivity of the brain and of the trigeminovascular apparatus. Activation of the trigeminovascular system, whether by neural impulses from the brain or humoral factors in the circulation, results in vascular headaches, while associated activity in the brain may produce such typically migrainous symptomatology as prodrome and aura, and nonspecific symptoms such as nausea, vomiting and dizziness. In this model specific diseases may gain access to the trigeminovascular apparatus, detonating it to produce vascular headaches and neurological symptomatology which may more or less exactly mimic migraine.