In addition to its important role in bone metabolism and calcium homeostasis an increasing number of beneficial effects are being attributed to vitamin D. Because of its suggested immunomodulatory capacity vitamin D deficiency or disturbance in the vitamin D metabolism might be a risk factor for the development of autoimmune diseases, such as multiple sclerosis; but supplementation with vitamin D might also be a therapeutic option. Substantial epidemiologic evidence indicates an association between vitamin D levels and risk of multiple sclerosis, suggesting vitamin D to be one of the long searched environmental factors for the development of this most common chronic inflammatory disease of the central nervous system. Less consistent are the available data for modification of the disease course in already established multiple sclerosis.This review highlights possible interactions between vitamin D and multiple sclerosis and focuses on its putative involvement in the pathogenesis and its possible role for treatment of multiple sclerosis. In particular the as yet insufficiently investigated therapeutic aspect is currently being addressed in several high quality clinical trials.