Natural killer (NK)/T-cell lymphoma associated with Epstein-Barr virus (EBV) in a patient infected with human immunodeficiency virus (HIV) is very rare. The authors encountered a case of NK/T-cell lymphoma in a 36-year-old man who presented with an ulcerative mass on both tonsils. During assessment, HIV positivity was noted. The EBV was detected by EBV-encoded RNA 1 messenger RNA in situ hybridization and polymerase chain reaction for EBV-encoded nuclear antigen 1. On immunohistochemical staining, the infiltrated lymphoid cells of the tonsils demonstrated positvity for CD3, CD56, UCHL1, and granzyme, a finding compatible with NK/T-cell lymphoma. The patient received radiation therapy and chemotherapy, but died as a result of opportunistic infection of invasive aspergillosis after tumor recurrence. An autopsy was done with the consent of the patient's family. To our knowledge, this is the first case in an HIV patient of NK/T-cell lymphoma of the tonsils associated with EBV, confirmed by autopsy. NK/T-cell lymphoma should be considered in the HIV-positive patients with an ulcerating tonsillar mass.