In the article literary data and data of own supervision on one of actual problems of modern dermatology- lichen ruber planus (LRP) of a mucous membrane of oral cavity (MMOC) are cited. Lesion of the mucous membranes is a characteristic feature LRP and is one of the most frequent manifestations of dermatoses, and may be related carried to “great” attributes which is of important diagnostic value. According to supervision of the authors, lesion of the mucous membrane was marked in 69 (32,2%) of patients with LRP. The authors registered a significant variety of clinical forms and variants of LRP course of the mucous membranes. As it is known, skin and mucous membranes are the basic organs where numerous pathomorphologic pathological manifestations of LRP are developed. But existence of both endo and exogenous mechanisms, influence on intertissue and interorgan immune relations, homeostasis, and metabolic processes this cannot but affect clinical polymorphism of skin lesions and those of mucous membrane of the oral cavity in LRP. To the authors’ opinion, hereafter it would be perspective to detail and clear up what factors of LRP and in what way affect skin lesions and those of mucous membranes, as well as under what conditions they are realized.