Ulcerative lesions of oropharyngeal mucous membranes are less commonly seen than other lesions in HIV infection and may be associated with mycotic, bacterial, and viral infection, as well as neoplasia. Differential diagnosis may be difficult because of the clinical similarity of ulcerations that can represent various causes. The term "atypical ulceration" has been suggested because it may be impossible to differentiate some of the oral ulcerations from each other. Iatrogenic ulceration is seen occasionally, as the consequence of chemotherapy or irradiation.