Chronic periodontitis in children and adolescents holds a lead place in morbidity pattern of dental pathology. Development of chronic periodontitis is accompanied by emergence of various complications in the maxillofacial region, leading to bite disturbance being of high relevance for pediatric patients. These and other complications are related to immune system immaturity in children and adolescents as well as virulence of microorganisms. However, the immunological changes developing in children with chronic periodontitis remain poorly studied. The aim of the work was to improve diagnostics of chronic periodontitis in children and adolescents based on informative parameters of systemic immunity and discriminative models taking into account such changes. We examined systemic immunity in 127 children and adolescents with chronic periodontitis, aged 12 to 16 years, by using flow cytometry and enzyme immunoassay. In control group, age-matched 108 patients lacking overt somatic and dental pathology were enrolled. Generation of mathematical models was carried out by using a discriminative approach, whereas informativeness was assessed in accordance with generally accepted formula. Relative and absolute count of peripheral blood CD13+ cells exert the peak informativeness holding the first and second ranking places with marked dominance of informativeness value for assessing relative amount of CD13+ cells are among immunological parameters in children with chronic periodontitis. High informativeness value evidencing about pronounced intensity of developed pathological changes and diagnostic significance for chronic periodontitis in children is intrinsic to the relative percentage of peripheral blood CD8+ cells being slightly lower than that one in absolute count of CD13+ cells. On the other hand, humoral immune-parameters were of lowest informative value among all analyzed immunological parameters in patients with chronic periodontitis serum referring to all antibody classes. Generated discriminative models for the most valuable immunological parameters ensure adequate medical diagnostics for chronic periodontitis in childhood. Diagnostic sensitivity for created mathematical models was high and reached 0.94, whereas diagnostic specificity - 0.92. Immunological examination of patients improves diagnostics of chronic periodontitis. It was found that patients with chronic periodontitis had lowered immune status peaking in decreased absolute and relative count of peripheral blood CD3+ lymphocytes. Finally, parameters of humoral immunity in children with chronic periodontitis were also reduced. © 2020 Saint Petersburg Pasteur Institute. All rights reserved.