Background. The significant prevalence and course of inflammatory periodontal diseases are associated not only with the presence of known bacterial agents, but also with changes in the body’s immune system that occur as a result of aging. Aim. To establish the relationship between the level of C-reactive protein in the blood and the course of localized periodontitis of traumatic etiology. Material and methods. During 2016–2019 169 patients with localized periodontitis of traumatic etiology (average age 56.44±0.14 years) of mild (102 people) and moderate (67 patients) severity at the Department of General Practice Dentistry of the North-Western State Medical University named after I.I. Mechnikov were examined. An in-depth dental examination, determination of periodontal indices, assessment of laboratory parameters (determination of high-sensitivity C-reactive protein, assessment and calculation of the entropy of the blood leukocyte formula), complex treatment using splinting with orthopedic structures in the main group (69 patients) and without it in the comparison group (57 people) were carried out. Statistical processing of data was conducted using the Shapiro–Wilk, Pearson, Kolmogorov–Smirnov tests, Fisher’s exact test and χ2 test, and calculation of relative risk. Results. Oral hygiene was good (hygiene index 0.54±0.18) and satisfactory (hygiene index 0.79±0.21) with mild and moderate severity, respectively. The local Mulleman–Cowell index was increased by 2.7 times (1.43±0.50) with mild severity and almost 4 times (2.31±0.33) with moderate severity of localized periodontitis of traumatic etiology compared with general index (0.52±0.12; 0.64±0.18). In localized periodontitis of traumatic etiology of moderate severity, an increase in the number of monocytes (8.7±2.12×109/l) and band neutrophils (5.4±1.47×109/l), an increase in the relative entropy of the leukocyte blood count (72.3±21.12%) compared with mild severity (62.8±14.9%; p=0.00089) were identified. With C-reactive protein concentrations ranging from 3 to 10 mg/l, the risk of developing localized periodontitis of moderate traumatic etiology increased by 1.74 times compared with C-reactive protein levels of less than 3 mg/l (p=0.0022). Conclusion. In localized periodontitis of moderate traumatic etiology, an increase in the number of band neutrophils and monocytes, as well as the relative entropy of the leukocyte blood count was detected. Preclinical increases in the concentration of C-reactive protein contribute to an increase in the severity of the disease. © Eco-Vector, 2023. All rights reserved.