The literature data and the finding of our studies on the analysis of the correlation between the level of parathyroid hormone and supply of vitamin D of children (n=107) of early age are presented in the article. The serum level of vitamin D in the analyzed group of children was 24.8 [17.6–32.5] ng/ml, the median of the parathyroid hormone was 21.0 [12.3–25.5] pg/ml. It has been established that children with optimal supply of vitamin D have significantly lower parathyroid hormone levels vs. the children with vitamin D insufficiency (25 (OH) D from 20 to 30 ng/ml) and deficiency (calcidiol values below 20 ng/ml). The correlation between the level of vitamin D and parathyroid hormone was r=-0.18, p=0.035. The best supply of vitamin D was found in children of the first year of life – 25 (OH) D concentration was 29.95 [16.2–40.3] ng/ml. The parathyroid hormone level (16.5 [10.7–23.8] pg/ml) in these children was reliably lower (p=0.05) vs. the children of the second and third years of life. A positive correlation was established between the age of patients and the parathyroid hormone level (r=0.2, p=0.05). Preventive doses of vitamin D were received by 42.1% of children. The blood serum concentration of 25 (OH) D in them was higher (32.7 ng/ml), and the parathyroid hormone level was significantly lower (14.9 pg/ml) vs. the children who did not receive cholecalciferol preparations (p<0.05). The obtained results demonstrate a strong correlation between vitamin D deficiency and the increased parathyroid hormone level that reflect the importance of these hormones in the regulation of calcium-phosphorus metabolism and the opposite role in bone tissue calcification.