CADASIL is an inherited arterial disease of the brain with an autosomal dominant pattern of transmission. The mapping of the affected gene in 1993 allowed us to describe the natural history of the disease. In some patients, the disease starts with attacks of migraine with aura at a mean age of 30 years. The most frequent clinical manifestations are subcortical transient ischemic attacks or completed strokes usually occurring between 40 and 50 years of age which are sometimes associated with severe mood disturbances. The disease leads about two decades later to death after a variable period of subcortical dementia associated with pseudobulbar palsy and urinary incontinence. In one given family, the severity of the clinical presentation varies among the affected subjects. MRI is always abnormal in symptomatic subjects. It shows more or less confluent hypersignals on T2-weighted images in white-matter and basal ganglia and hyposignals on T1-weighted images in the same regions corresponding to small infarcts. These signal abnormalities are even observed a long time before the onset of clinical manifestations as they are present in totally asymptomatic young family members. Histologic studies show a widespread palor of white-matter and multiple small infarcts in the white-matter and basal ganglia underlaid by a small artery disease of the brain. Electron microscopy studies show that the media of the white-matter and leptomeningeal small arteries is thickened by a granular, eosinophilic and non-amyloid material of undetermined origin close to the smooth muscle cells. These ultrastructural wall abnormalities have been observed in other arteries, particularly in muscular and skin arteries. Mutations of Notch3 gene located on chromosome 19 are responsible for the disease. The diagnosis should be discussed in subjects with a history of unexplained subcortical ischemic strokes, attacks of migraine with aura, mood disorders of subcortical dementia whenever associated with MRI signal abnormalities in white-matter and basal ganglia.