The world-wide incidence of vitamin D deficiency is high, independently of age. Multiple sclerosis is a chronic disorder, occuring in those who possess or are exposed to a combination of genetic and environmental risk factors. One of the environmental factors associated with the development is vitamin D. Vitamin D is an immunomodulatory agent, its role is verified in many of autoimmune diseases. Vitamin D inhibits IL-6, IL-17 and IL-23 secretions which are crucial in Th1 and Th17 differentiation and also decreases proinflammatorical cytokine production. Moreover it enhances the immunosuppressive IL-10 cytokine secretion and inhibits the T-reg cell development. These cytokines and cells are essential for the pathomechanism of multiple sclerosis. Data have shown, that the vitamin D levels above 100 nmol/l (40 ng/ml) is essential for the prevention of multiple sclerosis. Below this level the vitamin D supplementation is reasonable. In pregnancy, the vitamin D deficiency at the last two semester increases the risk for the multiple sclerosis of the infant. The optimal vitamin D level for multiple sclerosis patients is 100-150 nmol/l (40-60 ng/ml). There is no consensus for the role of vitamin D in multiple sclerosis yet, but until the achieving this, the diagnosis and the treatment of the vitamin D deficiency is crucial for scelrosis multiplex patients and in cases of elevated risk. Data shows, that in patient with multiple sclerosis the normal vitamin D level is suboptimal, however the exact role of vitamin D and doses must be clarified by interventional studies.