Notch signaling plays an essential role in vascular development and human vascular diseases. In adults, mutations of the Notch3 gene cause a hereditary vascular degenerative disease known as cerebral autosomal dominant arteriopathy with subcortical infarct and leukoencephalopathy (CADASIL). CADASIL is characterized by recurrent strokes and cognitive impairment. Over the past decade, the number of CADASIL patients increased significantly with improvements in genetic testing and other diagnostic tools, but the true prevalence of CADASIL is still underestimated, especially in Asia. Basic studies suggest that Notch3 is essential for the development and survival of the vascular smooth muscle cells, but the mechanisms by which Notch3 mutations become pathogenic are still unclear. This article reviews the clinical features and possible pathogenesis of CADASIL. Efforts to improve the diagnostic accuracy and define the role of Notch3 mutation in brain damage and clinical presentations of CADASIL should be continued.