Notch signaling is a very conservative system of cell-cell communications playing an essential role in vascular development and human vascular diseases. One of such diseases is a hereditary vascular degenerative disorder known as cerebral autosomal dominant arteriopathy with subcortical infarct and leukoencephalopathy (CADASIL). The disorder is caused by mutations in the NOTCH 3 gene encoding a transmembrane receptor of the same name present in vessels only on vascular smooth muscle cells and pericytes. The disease involves mainly small arteries and capillaries in which degeneration and loss of cells expressing Notch 3 receptor is observed. In the affected vessels accumulation of Notch 3 extracellular domain (N3-ECD) and granular osmiophilic material (GOM) containing N3-ECD are also found. Although pathogenesis of CADASIL is still unknown there are two main distinct hypotheses concerning its development. The first of them assumes that the disease is caused by dysfunction of the mutated Notch 3 receptor which acquires a new properties. According to the second hypothesis, CADASIL – as many other neurodegenerative diseases – is a proteinopathy due to accumulation of proteinaceous aggregates in vessel wall. This paper is an overview of recent findings concerning the role of Notch 3 in vascular biology and hypothetical participation of that signaling system in CADASIL pathogenesis.