Oral lichen planus (OLP) and recurrent aphtous stomatitis are the most frequent diseases of oral mucosa. Epidemiologic studies are demonstrating the frequency of 1-2 % in adult population. OLP is very frequently discussed in scientific literature. However, the etiology remains still unclear. Pathogenetic processes of OLP are partly elucidated. Changes involving the region of basal membrane are suggested to be the result of the apoptosis of keratinocytes. Apoptosis of keratinocytes is caused by CD8+Tlymphocytes. These cells are activated by TNFα. After the death of keratinocytes the stability of the basal membrane is changed, the basal membrane is splitted (teared). MMP 9 is involved in enhacing the process. Actually it is impossible to explore this knowledge in the treatment of OLP because the initial factor of the pathogenetic process is unknown.

        Key words: Oral lichen planus (OLP) - pathogenesis OLP - histological findings