Oral and labial lesions are usually the result of local disease but may be the early signs of systemic disease, including dermatological disorders, and in some instances may cause the main symptoms. This chapter mainly discusses disorders of the periodontal and mucosal tissues that may be related to skin disease and that may present at a dermatology clinic. It should be borne in mind that the professionals most competent in diagnosing and treating oral diseases are those with formal dental training and who are therefore in a position to understand the full complexities of the region. This chapter is divided into a brief discussion of the biology of the mouth, an overview of the more common signs and symptoms affecting specific oral tissues, discussion of the disorders of the oral mucosa of most relevance to dermatology and a tabulated review of oral manifestations of systemic diseases. Only the more classic oral lesions are illustrated. For reasons of space restrictions, diseases affecting the teeth, salivary glands, jaws or temporomandibular joints are not discussed in any depth.