School-aged children and their health conditions, in particular, deficient conditions are not less note worthy than in younger children, while the recognition of present low vitamin D provision in children of all age groups has not still resulted in implementation of mass prophylaxis of hypovitaminosis D. There are several factors on which blood concentration of 25 (OH) D-calcidiol-depends. However, it is evident that among numerous factors we should orient on several most significant and develop correction scheme for the deficient condition in every region. Aim: to assess vitamin D levels in adolescents residing in Moscow, to correct their calcidiol status based on a baseline blood concentration of the transport metabolite. Materials and methods: 769 adolescents aged 11-18 years were examined and their blood concentration of 25 (OH) D was determined. Then, 218 patients were randomized to 2 groups: the treatment group received food supplement "Minisun ® Vitamin D 3 " in tablets, the control group received placebo. Cholecalciferol dosage was prescribed depending on the baseline calcidiol level in patients. The study continued for 6 months, after that blood was re-withdrawn for calcidiol level. Results: low calcidiol provision was observed among school children: median 25 (ОН) D was 16.3 [11.4-20.8] ng/mL, only 5.2% of patients had normal blood concentration of calcidiol. There-examination showed significant differences in vitamin D status in the treatment and control group, in the meantime, during cholecalciferol supplementation, median 25 (OH) D in patients of the treatment group was increased from 16.2 [12.25-19.3] ng/mL to 24.2 [21.05-26.4] ng/mL (p < 0.001). Conclusions: the larger part of child population-70.6% has 25 (OH) D concentration < 20 ng/mL, cholecalciferol doses used in the study allow eliminating calcidiol deficiency and overcome the boundary of 20 ng/mL, but for normalization of vitamin D status in blood of adolescents residing in Moscow higher dosages shall be used which is to be confirmed by further studies.