Oral lesions such as candidiasis, Kaposi's sarcoma, hairy leukoplakia, herpes simplex infection, and ulcerative periodontitis are associated with HIV infection and may be the primary presentation in persons with undiagnosed HIV. We report a clinical case in which an 80-year-old man presented with an oral ulcer with morphological signs of immuno-suppression. The patient was perceived to be at low risk of HIV infection and thus, diagnostic HIV testing was delayed until subsequent development of Kaposi's sarcoma on the skin.