The role of vitamin D (Vit. D) in bone metabolism is well known. It has recently been described that Vit. D exerts immunoregulatory activity, anti-proliferative and pro-differentiation mediated by intracellular receptors of the vitamin (VDR), so it seems to prevent the onset of some cancers (colon, prostate, etc.) and finally has a role in the evolution of some skin dermatoses such as psoriasis and atopic dermatitis. It well known that the presence of low blood levels of Vit. D, associated with the polymorphism of the VDR gene, may correlate with some inflammatory diseases such as also indicated by some authors, according to which the metabolites of Vit. D would be the clinical markers of certain diseases chronic and autoimmune diseases.