The purpose — to determine the level of vitamin D availability and to evaluate the effectiveness of its supplementation in children who have been on a dairy-free diet for a long time. Material and methods. At the first stage of the study, the availability of vitamin D and calcium in children were assessed. 62 children were examined who had been on a dairy-free diet (group I). The control group consisted of 30 conditionally healthy children who did not keep any restrictive diets. At stage II, a scheme of vitamin D supplementation was proposed, which consisted in taking an aqueous solution of cholecalciferol in a therapeutic dose during one month, depending on the initial level of calcidiol in blood serum: at the level of 11–20 ng/ml (vitamin D deficiency), 3000 IU/day was prescribed, at the level of 21–29 ng/ml (insufficient vitamin D) — 2000 IU/day, switching to the dose of 1000 IU/day. Children with adequate provision of vitamin D were prescribed a prophylactic dose of cholecalciferol — 1000 IU/day. Subgroup Ia consisted of 32 children who received cholecalciferol supplementation. Subgroup Ib included 30 children who had no supplementation. The importance of daily consumption of foods rich in calcium and vitamin D was explained to children of both subgroups and their parents. The assessment of vitamin D and calcium availability was repeated after 4 months of follow-up. Results. The proportion of children with insufficient vitamin D in group I was 62.9%, which was statistically significantly higher (p < 0.001) relative to the proportion of children with normal concentration or deficiency of vitamin D in blood serum. A decrease in serum calcium levels among patients of this group was found in 64.5% of children, which was statistically significant (p < 0.001) relative to children of the control group. After the course of cholecalciferol supplementation in subgroup Ia, insufficient vitamin D was found in 18.8%. Normal micronutrient availability was established in 81.2%. Among children of subgroup Ib, the proportion of children with normal vitamin D availability at the control visit was 33.3%, which was less (p < 0.01) relative to subgroup Ia. Normal values of calcium in blood serum against the background of complementation were found in 78.1% of children of subgroup 1a and in 36.7% of children in subgroup 1b. Conclusions. For children who follow a dairy-free diet, insufficient vitamin D and calcium levels are characteristic. Supplementation with an aqueous solution of cholecalciferol has shown its effectiveness in normalizing the level of calcidiol and calcium in the blood serum of children on a dairy-free diet.