Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) begins with migraine with aura in approximately one‐third of the patients. More severe symptoms of recurrent strokes usually appear at 30–50 years of age. However, well before the first stroke, CADASIL may be diagnosed on the basis of characteristic hyperintensities in T2‐weighted magnetic resonance images. Multiple lacunar infarcts located mainly in the basal ganglia and frontal white matter lead to a cognitive decline and finally to dementia. These infarcts result from a thickening and fibrosis of the walls of the small and medium‐sized penetrating arteries with consequent obliteration and/or thrombosis. Although the symptoms are almost exclusively neurological, the arteriopathy is generalized. Thus, basophilic, periodic acid–Schiff‐positive and, in electron microscopy, osmiophilic material accumulates between degenerating smooth muscle cells. This occurs even in dermal arteries, which renders skin a useful target for diagnostic biopsy. Presently, no specific therapy is available. CADASIL is caused by missense point mutations in the Notch3 gene, which encodes a transmembrane receptor protein. Each gene defect leads to either a gain or loss of a cysteine residue in the extracellular, N‐terminal domain of the molecule, which most probably results in conformational alteration. The function of Notch3 in adults and the pathogenesis of CADASIL are still unknown.