Multiple sclerosis (MS) is a chronic idiopathic inflammatory disease of the central nervous system characterized by demyelinating lesions in the brain and the spinal cord. It most commonly affects young adults, with a peak incidence between the age of 25 and 35 years and is a significant cause of disability in this age group.The cause of the disease is unknown but the current findings argue in favor of autoimmune pathogenesis. Numerous epidemiological and experimental studies have shown that both genes and environmental factors play a role in the etiology of MS. Of the environmental factors the most investigated are infection, smoking and lack of vitamin D. Vitamin D belongs to fat-soluble group of vitamins and plays several roles, of which the maintenance of bone health and influence on metabolism of minerals is the best known. In addition, vitamin D can modify the immune response, cell proliferation, differentiation and apoptosis. Vitamin D deficiency is associated with numerous diseases, including MS. Geographical distribution of the disease refers to the role of the vitamin D in the first place. Also numerous studies, which are based on the study of its immunomodulatory properties, influences on the expression of certain genes and the study of its role in the animal model of MS, have shown that it undoubtedly plays the role in the onset and course of the disease. Some studies have shown that vitamin D has a role in preventing MS. However, large studies which should confirm whether and how taking vitamin D supplements can prevent the disease, have only just begun. Results of the studies that have dealt with the issue of the role of vitamin D in the treatment of patients who have developed MS are rather ambiguous, but they still speak in favor of its positive effects. Furthermore, vitamin D is now part of the standard therapy for MS to which contributes the fact that it is natural, safe and inexpensive. Future studies will clarify whether taking supplements of vitamin D has a direct effect on the disease course and will answer the question of how much vitamin D is required for the treatment, as well as its optimal level in the blood of patients with MS.