Vitamin D is a factor that plays a significant role in calcium-phosphate balance. It has an effect on bone metabolism and also has modulator and anti-inflammatory activity. It is claimed that vitamin D inhibits immunological reactions with Th1 and Th17 lymphocytes. The influence of vitamin D on Th2 lymphocytes is not clear. The main effect of vitamin D is probably the activation of Treg lymphocytes. It was observed that vitamin D had a beneficial influence on diseases connected with excessive activation of Th1 lymphocytes, such as multiple sclerosis, rheumatoid arthritis, non-specific enteritis, diabetes type 1 or psoriasis. The role of vitamin D in allergic diseases, in which increased activation of Th2-dependent reactions are of great importance, is controversial. However, due to a wide range of vitamin D activity, this view seems to be simplified. A beneficial effect on the course of allergic diseases was observed in up-to-date studies although the role of vitamin D in their pathogenesis has not been explained yet. On the basis of recent studies and well-known mechanisms of vitamin D activity on particular elements of the immunological system, the influence of vitamin D on the course of chosen allergic diseases, such as allergic asthma, atopic dermatitis and allergic rhinitis was presented considering the possibility of contribution of allergen-specific immunotherapy.