Subject. The review which has been carried out allows us to consider the issues of etiopathogenesis of lichen planus and lichenoid lesions of the oral mucosa adapted to the modern classification. The analysis of clinical features must be carried out with an emphasis on differential diagnosis. The aim is to conduct a systematic analysis of modern native and foreign literature sources to determine some features of the etiology and pathogenesis of lichen planus and lichenoid reactions of the oral mucosa, depending on risk factors. Methodology. The search for research papers on the etiology and pathogenesis of this dermatosis was carried out using the following databases: PubMed, Web of Science, Medline, elibrary.ru, Scopus in the period from 2010 to 2021, and the review includes selected significant publications for the period from 2015 to 2021. The following keywords were used: lichen planus, oral lichenoid lesions, prevalence, clinical symptoms, clinical forms, risk factors. Special attention was paid to articles published in peer-reviewed scientific publications. Research methods used in the analysis process: content and descriptive-analytical analysis. As a result of an electronic search, 74 publications were found. The conducted research has a wide geography: Austria, Australia, Belarus, Great Britain, India, Spain, Italy, Iran, Yemen, China, Korea, Russia, Romania, USA, Saudi Arabia, New Zealand, Taiwan, Thailand, Tehran, Croatia, Scotland, Philadelphia, Japan. Results. Among all the pathological processes that were diagnosed on the oral mucosa, lichen planus occurs on average from 35 to 70% of cases, while only isolated or oral forms are diagnosed on average from 50 to 75% of cases of examinations, the frequency of simultaneous lesions of the mucous membranes and skin is 23-28.6%. The pathogenesis of the studied pathology has significant differences depending on the diagnosed form of lichen planus, or manifestations of lichenoid lesions. Conclusions. In a comprehensive examination of these patients, it is very important to analyze not only the clinical features of oral forms of lichen planus, but also to evaluate the topographic location of morphological elements, their symmetry, and size. These data together allow for a differentiated approach in making an accurate diagnosis. The diagnostic process of oral forms of lichen planus and lichenoid lesions also includes the identification of general somatic diseases, the assessment of local risk factors, and the identification of the relative frequency and intensity of their clinical forms. The main diagnostic feature that allows you to distinguish lichenoid lesions from lichen planus is the fact that the elimination of the factor that provoked the symptoms leads to the disappearance of the damage.