Clinical and microbiological evaluation of periodontal tissues was performed in 74 patients with type 2 diabetes mellitus. Possible relationships between the severity of chronic generalized periodontitis and the qualitative composition of the microbiota of periodontal pockets are revealed. The main group included patients with chronic generalized periodontitis of various severity and associated type 2 diabetes mellitus (n=41). The control group included patients with chronic generalized periodontitis of various severity without type 2 diabetes mellitus (n=33). The periodontal status of the patients of the main group is characterized by a more pronounced inflammatory reaction of periodontal tissues in comparison with the patients of the control group, which is confirmed by the data of a clinical examination and an index assessment of the state of periodontal tissues (PMA, CPITN, BOP indices). Patients of the main group had P. gingivalis and T. denticola detected in their periodontal pockets, dominating among the studied periodontal pathogens (70.7% and 68.3% of cases, respectively). With an increase in the severity of chronic generalized periodontitis, increasing dynamics of the detection frequency of P. gingivalis, T. denticola, and P. intermedia was recorded. During the development of periodontitis in patients with type 2 diabetes mellitus, with an increase in the severity of the disease and the progression of inflammatory changes in periodontal tissues, a decrease in the frequency of detection of single periodontal pathogens is observed along with an increasing tendency to their grouping into different complexes.