Purpose: to assess the severity of vitamin D insufficiency or deficiency in different degrees of obesity, in the presence or absence of insulin resistance in patients with type 2 diabetes mellitus. Object and research methods. Totally 148 patients with type 2 diabetes mellitus in a state of compensation (glycated hemoglobin <7.5%) were included in the study. They were divided into groups comparable in sex and age according to body mass index: normal, overweight, obesity 1, 2, 3 degrees. Determination of the level of vitamin D supply was carried out using chemiluminescent immunoassay. Results. Statistically significant decrease in 25-hydroxyvitamin D levels as body mass index increased was observed. These indicators were significantly inversely proportional. Patients with insulin resistance syndrome were worse supplied with vitamin D. Conclusion. Taking into consideration the unsatisfactory vitamin D supply of patients with type 2 diabetes mellitus in Ukrainian population, preventive and therapeutic measures to normalize the concentration of 25-hydroxyvitamin D can be recommended, which will potentially have a positive effect on restoring insulin sensitivity. Weight loss in patients with type 2 diabetes mellitus will also contribute to improving the vitamin D supply.