Allergy constitutes an important problem in today’s world. Atopy, excessive IgE antibodies genetically determined production predisposition is usual basis for allergy. Atopic dermatitis, asthma, allergic rhinitis, allergic conjunctivitis, enteral allergy’s and nettle-rashes are the most common allergic diseases of child development age. Genetic factors, viral infections and environmental factors have proven influence in development of atopic diseases. Recently there is large interest in vitamin D3 (cholecalciferol) role in development of atopic diseases. Oral forms of vitamin D3 and its active metabolites and synthetic analogs are traditionally used to regulate calcium-phosphoric homeostasis. Vitamin D is typical inactive biologically prohormone created in skin tissues from steroid precursor. Two degrees of enzymatic hydroxylation (in liver and in kidneys) are needed to form main hormonally active form. 1.25(OH)2D is the most biologically active hormone. 25(OH)D and 1.25(OH)2D are marked in diagnostic goals. Large populations research point out strict correlation with long lasting vitamin D deficiency and metabolic disorders. Cholecalciferol serum deficiency increases autoimmune and infectious diseases risks. Vitamin D receptor (VDR) cholecalciferol stimulation is responsible for its actions exceeding mineral management. Children atopic diseases risk and low vitamin D pregnant women uptake correlation has been suggested. Recent researches show that cholecalciferol is autoimmune diseases immunoprotective factor, it limits Th1 immunological response and moves it into Th2 response domination. According to same quoted publications it appears that proper vitamin D supplementation can decrease risks of atopic and autoimmune diseases. There are also data suggesting increase of excidence of allergic diseases in case of excessive vitamin D supplementation.