A 36-year-old man with HIV presents with a painful oral ulceration that he noticed about 2 weeks ago. The lesion has increased in size and become more painful (Figure 1). He has no other new lesions. He has consistently maintained suppressed HIV RNA levels (<50 copies/mL) on the antiretroviral regimen of dolutegravir plus tenofovir DF-emtricitabine. A CD4 count obtained 4 months ago was 318 cells/mm³. Serologic testing for syphilis is negative, polymerase chain reaction (PCR) test for herpes simplex virus (HSV) is negative, but a PCR for mpox is positive.