Introduction: Diabetes mellitus and COVID-19 are nosologies that pose new challenges in the field of medicine, and after their combination, have already outlined their importance and potentially large impact on the health of people around the world. Each of these pathologies individually has a significant impact on the lives and well-being of patients, and together they create complex conditions for medical practice and healthcare organization. The study of the mutual influence of diabetes mellitus and COVID-19 on the clinical picture, features of the course, diagnosis and treatment of patients is of great importance and relevance for both the scientific community and applied practical medicine, and its continuation and expansion is a scientific and public need. Materials and Methods: А total of 53 patients with COVID-19 were examined. Their medical records were reviewed. To assess the clinical parameters, epidemiological data, physical and psycho-emotional state of patients, the author's own questionnaire "Form of Communication-1" was created and used. Based on the data obtained, statistical indicators were calculated: Pearson's test for qualitative indicators, Mann-Whitney U test was used as a non-parametric analysis method, Student's t-test for values that corresponded to the normality of distribution, respectively. Results: Patients with COVID-19 were divided into two groups: with diabetes mellitus (20 patients, 37.7%) and without this pathology (comparison group) (33 patients, 62.3%). Most of those studied were women (57%), aged (59.2 ± 12.5) years. Patients were hospitalized on days 4-5 of the disease. Among the concomitant pathologies, arterial hypertension and coronary heart disease were more frequently detected in the group of patients with diabetes mellitus (85% each), in the comparison group (55% and 52%, respectively (p < 0.05). The coronavirus disease began acutely with chills and fever up to (38.3±0.18) °C. Generalized weakness was experienced by 96 % of patients. Among the complaints in the comparison group, ague (33 %) and hoarseness of the voice (52 %) prevailed (p < 0.05). Severe COVID-19 was observed in 85% of patients with diabetes mellitus, and in the comparison group - in 33% of patients. On the contrary, moderate severity prevailed in the comparison group (64 % of patients) (p < 0.05). The blood glucose level in patients with COVID-19 in the setting of type 2 diabetes was (9.9 ± 6.8) mmol/L and was higher than in the comparison group (5.8 ± 1.4) mmol/L, indicating hyperglycemia due to impaired glucose tolerance (p < 0.05). Conclusions: Women (57%) of middle age (59.2 years) predominate among patients. Severe COVID-19 predominates in the group of patients with diabetes mellitus. The clinical picture is not significantly different in the compared groups, but laboratory data (elevated C-reactive protein, changes in platelet size, elevated levels of alanine aminotransferase, aspartate aminotransferase, gamma-glutamyl transpeptidase, urea, creatinine), objective symptoms (changes in general condition, severe course, auscultatory abnormalities) indicate more pronounced changes in patients with COVID-19 and diabetes mellitus. SARS-CoV-2 induces changes in glucose metabolism and contributes to the severity of COVID-19, which in turn leads to hypercytokinemia, cytokine storm, tissue and airway damage.