The chronic periodontitis in children is frequently complicated by development of periapical abscess under inadequate conservative therapy. However, prognostic models of estimation of probability of its development are lacking. The purpose of study is to develop regression models of prognostication of periapical abscess under chronic periodontitis in children according indices of peripheral blood and systemic cellular immunity. The chronic periodontitis complicated with periapical abscess is analyzed in 120 children aged from 8 to 15 years. The prognostication of periapical abscess was implemented by stepwise regression technique using parameters of blood and systemic cellular immunity. The mathematical models are developed for prognostication of periapical abscess in children with chronic periodontitis on the basis of indices of peripheral blood and systemic cellular immunity permitting to prognosticate development of the given complication with needed quality. The prognostication periapical abscess requires using the given models, absolute number of lymphocytes, percentage of stab bond neutrophils, ESR, absolute number of T-lymphocytes in blood, T-helpers, T-suppressors and relative content of T-suppressors. © 2018 Izdatel'stvo Meditsina. All rights reserved.