Human herpes virus type 8 (HHV8) has been strongly associated with Kaposi sarcoma, primary effusion lymphoma (PEL), and Castleman's disease. To our knowledge, infection by this virus has not been strongly associated with other hematopathologic malignancies. We examined five oral cavity lymphomas from men with AIDS for HHV8 and HIV-1 by reverse transcriptase in situ polymerase chain reaction, as well as for Epstein-Barr virus (EBV) (EBER-1, -2) using in situ hybridization and HHV8 protein with immunohistochemistry. Four of these tumors were plasmablastic lymphomas; the final case was diffuse large B-cell lymphoma. Most of the neoplastic cells in these five lymphomas contained HHV8 RNA and protein. Further, the four plasmablastic lymphoma cases had tumor cells that contained EBV. HIV-1 RNA was not detected in the tumor cells but was noted in surrounding benign T cells. In comparison, HHV8 RNA was not detected in any of the five oral cavity lymphomas from people who did not have acquired immunosuppression nor in five lymphomas from AIDS patients that were located at a site other than the oral cavity. It is concluded that oral cavity lymphomas from people with AIDS are strongly associated with infection by HHV8 and EBV. Given the poor prognosis of oral cavity lymphomas in immunocompromised patients, therapy directed against the HHV8 and EBV infection may be of therapeutic value.