Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a dominantly inherited small artery disease that leads to dementia and disability in mid-life. The clinical presentation of CADASIL is variable between and within affected families and is characterized by symptoms including migraine with aura, subcortical ischemic events, mood disturbances, apathy, and cognitive impairment. The mean age at onset of symptoms is 45 years, with variable duration of the disease ranging from 10 to 40 years. In 1996, linkage studies mapped and identified mutations in the NOTCH3 gene on chromosome 19 as causative in CADASIL. Head magnetic resonance imaging (MRI) is always abnormal in participants with NOTCH3 mutations after age 35. Magnetic resonance imaging shows on T2-weighted images or fluid attenuation inversion recovery (FLAIR) sequence, widespread areas of increased signal in the white matter associated with focal hyperintensities in basal ganglia, thalamus, and brainstem. The pathologic hallmark of CADASIL is the presence of electron-dense granules in the media of arterioles that can be identified by electron microscopic evaluation of skin biopsies.