Many skin diseases may affect the oral and genital mucous membranes but involvement is generally uncommon. Mucous membranes are most often affected by lichen planus and less frequently by psoriasis or lupus erythematosus. Macroscopic changes may vary from increased vulnerability, erythema and erosions to leukoplakia. Subjective symptoms of burning sensations or localized pain must be distinguished from underlying psychiatric disorders. Furthermore, neoplasia may complicate chronic lichen planus. Therefore, depending on the location and extent of mucous membrane symptoms, both local and systemic therapy may be necessary. Short- and long-term dermatologic care are required.