This is a single center, prospective, open label, single arm, investigator initiated pilot study investigating the effect of alitretinoin on severe lichen planus with mucosal manifestations. The target population comprises patients with MLP for at least 3 months, with or without LP lesions on other areas of the skin, who are refractory to topical therapy and standard skin care, and who are otherwise in good health. Patients will be recruited at the outpatient clinic of the dermatology department, University hospital Zurich.The planned duration of the study is 2 years. A total of 20 patients will be included. Patients who meet enrolment criteria will receive 30mg alitretinoin, given orally as gelatin capsules, once daily for 24 weeks. Dose interruptions are permitted in response to adverse effects, consistent with use of retinoids and the product label.