Human immunodeficiency virus (HIV)-related opportunistic infections are defined as infections that are more frequent or more severe because of immunosuppression mediated by a patient's HIV infection. These include infections with fungal, bacterial and viral aetiologies. Only a subset of these infections presents with oral manifestations but these are common, and effective treatment requirements may be different than in HIV-negative patients. Non-Hodgkin's lymphoma and Kaposi's sarcoma are the two major acquired immune deficiency syndrome (AIDS)-defining cancers. Other non-AIDS-defining cancers include non-small cell lung cancer, Hodgkin's lymphoma, oropharyngeal cancer, hepatocellular carcinoma and squamous cell carcinoma of the anus, vulva and penis. Recurrent aphthous ulcers are generally seen in HIV patients with a previous history of recurrent aphthous stomatitis. Patients will often report an increase in the frequency and severity of episodes.