Human papilloma viruses (HPV) can be detected in different epithelia with the help of the polymerase chain reaction (PCR). The role of HPV in the development of anogenital cancers has been intensively studied, and current evidence shows that most cervical cancers are associated with so-called high risk HPV types (e.g. HPV 16 and 18). HPV-infections can also be demonstrated in oral premalignant lesions and squamous cell carcinomas. Depending on the sensitivity of the detection method, 40-67% of leukoplakias, 2.5-76% of squamous cell carcinomas and 0-87% of cases of lichen planus were described to be infected with HPV 16 or 18. Whether lichen planus can be considered as a premalignant lesion is still controversial. By the use of PCR and hybridization we found infections with the high risk HPV types 16, 18 and 31 in 42% (3/7) of the patients with lichen planus. Further investigations with a higher numbers of cases in combination with the analysis of the viral gene expression as well as the clinical and histological control of the corresponding regions are necessary. The aim of these studies is to find out the prognostic value of the HPV infection for this facultative premalignant disease.