Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) often begins with migraine with aura. Recurrent strokes usually appear between 30 and 50 years of age. The arteriopathy develops slowly, resulting in destruction of smooth muscle cells and thickening and fibrosis of the walls of small and medium-sized penetrating arteries with consequent narrowing of the lumen. This impairs cerebral blood flow, visible in PET, and produces characteristic white-matter hyperintensities in T2-weighted MRI on the basis of which CADASIL may be diagnosed well before the first stroke. Multiple lacunar infarcts, mainly in the frontal white matter and basal ganglia, lead to progressive permanent brain damage manifested as cognitive decline and finally as dementia. At present, no specific therapy is available. Infarcts result from thickening and fibrosis of the walls of small and medium-sized penetrating arteries with consequent obliteration and/or thrombosis. Although the symptoms are almost exclusively neurological, the arteriopathy is generalized and diagnosis can be made on the basis of accumulation of pathognomonic basophilic, PAS-positive and in electron microscopy osmiophilic material between degenerating smooth muscle cells in dermal arteries. CADASIL is caused by missense point mutations in the Notch3 gene, which encodes a transmembrane receptor protein with an important signaling function during development. The gene defects lead to either a gain or loss of a cysteine residue in the extracellular N-terminal part of the molecule, most probably causing a conformational and functional alteration. The function of Notch3 in adults and the definite pathogenesis of CADASIL are still unknown, but interestingly its intramembranous proteolytic cleavage may be regulated or implemented by presenilin similarly as cleavage of amyloid precursor protein in Alzheimer's disease.