Crohn's disease (CD) and ulcerative colitis (UC) are the main forms of inflammatory bowel disease (IBD), chronic relapsing-remitting inflammatory conditions of uncertain origin affecting the gastrointestinal tract.Much effort has recently been made both in defining the mechanisms underlying the development of IBD, and in broadening the spectrum of effective treatment. Substantial progress has been made in characterising immune-cell populations and inflammatory mediators in IBD.1,25-Dihydroxyvitamin D3 [1,25(OH)2D3], the bioactive form of Vitamin D3, besides having well-known control findings of calcium and phosphorus metabolism, bone formation and mineralization, also has a role in the maintenance of immune- omeostasis. The immune-regulatory role of vitamin D affects both the innate and adaptive immune system contributing to the immune-tolerance of self-structures. Impaired vitamin D supply/regulation, amongst other factors, leads to the development of autoimmune processes in animal models of various autoimmune diseases, including IBD. The administration of vitamin D in these animals leads to improvement of immune-mediated symptoms. Future studies now need to focus on the potential of vitamin D and its derivatives as therapeutic adjuncts in the treatment of IBD.