question: The review is devoted to the analysis of modern ideas about the role of bacteria Filifactor alocis in the etiology of chronic periodontitis. The study of these bacteria, discovered in 1985, is complicated by the difficulty of their detection with cultural methods. According to modern researches, the bacteria F.alocis with good reason can be included in the red complex of periodontal pathogens as the most important pathogens of chronic periodontitis. F.alocis is a synergist of such a key pathogen Porphyromonas gingivalis, as well as a frequent satellite of Fusobacterium nucleatum and, somewhat less frequently, Aggregatibacter actinomycetemcomitans. F.alocis is practically not found in healthy people (except for smokers), with a high frequency accompanies the aggressive course of periodontal disease, and also recorded in endodontitis. Due to the ability to participate in the metabolism of arginine, expressed protease activity, a wide range of virulence factors, F.alocis not only colonizes the periodontal tissues, but also significantly affects the formation of the community of periodontal microorganisms (including viruses), contributing to their invasion of epithelial tissues. F. alocis has a number of unique properties, including resistance to oxidative stress conditions in the home defeat, induction of apoptosis of epithelial cells, extracellular matrix degradation of periodontal tissues, activation of proinflammatory cytokines formulation in sites of its presence, suppression of protective reactions of neutrophilic granulocytes, inhibition of the process of complement activation.