The oral cavity is the site of diverse manifestations of iatrogenic disease. Mucosal pigmentations, gingival hypertrophy, ulcerations, mucositis and xerostomia are easily identifiable, but may simulate diseases that are well known to localise to the oral cavity, such as aphthous ulcers or lichen planus. Drug therapies are at the origin of the greatest number of these lesions. A rigorous inquiry into the characteristic oral lesions permits, in the majority of cases, the establishment of this relationship.