The endothelium plays an important role in the maintenance of vascular homeostasis, the tone and anatomical structure of the vascular wall. It is an essential component of the blood-brain barrier. In adverse conditions, damaged endothelium initiates many pathological processes in the human organism and plays a key role in the pathogenesis of a number of systemic diseases including multiple sclerosis. In this review, we discussed in detail the concepts of structural and functional features of a healthy endothelium and endothelial dysfunction, and present the basic theory of the damage mechanism of the blood-brain barrier and the role of endothelial cells, adhesion molecules, cerebral hypoperfusion in multiple sclerosis.