Periodontal tissue diseases remain one of the urgent problems in modern dentistry due to their high prevalence and the number of complications after treatment. The prolonged asymptomatic course of chronic forms of periodontitis causes an increase in destructive processes not only in periodontal tissues and alveolar bone, but also contributes to the resorption of cementum and root dentin, which causes the formation of bone pockets, called furcation defects. Involvement in the pathological process of the zone of divergence of the roots significantly complicates the course of the disease, diagnosis, treatment and prognosis. The complexity of diagnosis, the variability of treatment methods depending on the overall clinical picture and the high percentage of tooth loss when the furcation area is involved in the pathological process determine the relevance of the research topic. Purpose: to study the features of chronic periodontitis complicated by furcation defects and to identify the main causes of these defects. Materials and Methods: the analysis of domestic and foreign publications placed in the eLibrary and PubMed databases was carried out by keywords. Results. The analysis of literature data on the features of chronic periodontitis complicated by furcation defects is carried out, the issues of the etiology of this pathology are considered. Conclusion. It is shown that the treatment of chronic apical periodontitis complicated by furcation defects is one of the important problems of dentistry, which is determined by the significant prevalence of the disease and the incidence of complications after treatment. The most common etiological factor in furcation lesions is microbial invasion, which causes an inflammatory process, the progression of which leads to bone resorption in the area of the furcation arch of the teeth. Also, the etiological factors of periodontal pathogenic genesis, endodontic lesions, fractures, iatrogenic factors, as well as anatomical features contribute to the involvement of furcation.