Recently identified, CADASIL is a diffuse disease of small arteries, predominating in the brain. It starts during mid-adulthood and is characterized by recurrent ischemic events (transient or permanent), attacks of migraine with aura, severe mood disorders, subcortical dementia and, at MRI, a white spread leukoencephalopathy. There is so far no specific treatment and death occurs after a mean of twenty years. CADASIL is an autosomal dominant condition and the gene Notch 3 is located on chromosome 19, in the same region as another neurological disorder, familial hemiplegic migraine.