Lichen is a chronic, mucocutan disease with unknown origin. Oral lesions are usually bilateral, the most frequent location of the reticular form is the posterior part of the buccal mucosa. It undergo only rarely spontaneous remission, and it has a potential to turn into malignant tumor. It is hypothesized that due to an antigen-specific mechanism, auto-cytotoxic T-cells infiltrates the affected region. T-lymphocytes induces apoptosis in the keratinocytes of the basal epithelium. Since etiology is unknown, there is no cure for lichen. The symptomatic treatment has been focused on reducing the subjective discomfort and to maintain or improve the quality of life. The main course of therapy are topical retinoids, locally given steroids, but immunosuppressive therapies have been also tried. Data about exact etiology, diagnostical criteria and effective treatment are still limited. Therefore, besides the early detection of the disease, symptomatic treatment, and the close observation of dysplastic lesions is recommended.