In patients with acquired immunodeficiency syndrome (AIDS), primary central nervous system lymphoma (PCNSL) is now the most common noninfectious intracranial mass lesion and the fourth leading cause of death. Most cases of PCNSL are B-cell in origin and are only rarely of T-cell origin. We report the first complete clinical description of T-cell PCNSL in a patient with AIDS. This patient underwent stereotactic biopsy of a cerebellar lesion that demonstrated T-cell lymphoma by immunohistochemical staining. The patient died from opportunistic infection after partial radiation therapy. Complete autopsy revealed no evidence of residual T-cell lymphoma. The authors compare T-cell PCNSL in patients with and without AIDS, and discuss differences between T-cell and B-cell PCNSL. In conclusion, T-cell PCNSL can occur in patients with AIDS. The tumor is often located infratentorially and appears to be radiosensitive. However, the patient's survival is short because death is usually caused by opportunistic infection rather than mass effect from lymphoma.