The proven relationship between the frequency of influenza and acute respiratory infections in children with vitamin D deficiency and the data on the relationship between a high mortality rate from SARS-CoV-2 in patients with low levels of vitamin D in the body under conditions of a forced sharp decrease in the level of insolation in the period from March 11, 2020 dictated the relevance assessing the vitamin D supply of children and adolescents in educational organizations of the city of Ulan-Ude. Purpose of the study: to assess the vitamin D supply of children and adolescents living in the city of Ulan-Ude. Methods: in a non-randomized, single-center, transverse (one-stage) uncontrolled comparative study, the concentration of 25(OH) vitamin D – 25(OH)D – in the blood serum of children and adolescents in Ulan-Ude was studied from May 22 to May 24, 2020. Moderate vitamin D deficiency (deficiency) was determined when the content of 25(OH)D was in the range of 20–30 ng/ml, the deficiency was within the limits, and the severe deficiency was <10 ng/ml. Results: assessment of vitamin D provision was carried out in 60 children aged 10 to 17 years (15 [11; 16] years), of which 19 boys, 41 girls. Children were divided into 2 groups depending on age: 10–11 years old (grade 5) (n=27) and 15–17 years old (grades 9–11) (n=33). Deficiency of vitamin D was found in 4 (15%), 11 (33%); deficit – in 19 (70%), 18 (55%); severe deficiency – in 2 (7%), 4 (12%), respectively. Along with low indicators of the provision of children and adolescents in the city of Ulan-Ude, an even lower provision of children and adolescents of Buryats was noted. The concentration of vitamin D in Buryat children and adolescents below normal (less than 30 ng/ml) was found in 35 (100%) children and adolescents, deficiency – in 8 (23%) children, vitamin D deficiency – in 21 (60%) children and severe deficiency – in 6 (17%). A statistically significant difference in the content of 25(OH)D between children and adolescents of Russian nationality and Buryats was revealed (p=0,0056). Evaluation of the diet showed that the frequency of consumption of fish as a source of vitamin D by children and adolescents is low. Conclusion: there is a high incidence of vitamin D deficiency and deficiency, which amounted to 97% in the examined children and adolescents living in the city of Ulan-Ude, more pronounced in Buryat children and adolescents, which requires organizational measures to replenish the vitamin D deficiency.