Lymphoproliferations associated with Epstein-Barr virus (EBV) commonly arise in settings of immune dysfunction, including human immunodeficiency virus (HIV) infection. In this study, EBV was associated with 39 of 59 (66%) HIV-related systemic lymphomas. Unlike the lymphoproliferations that arise in the setting of transplantation, the HIV-related lymphomas were monoclonal, as evaluated by Ig heavy chain rearrangements and EBV termini analysis, and associated (40%) with c-MYC rearrangements. Furthermore, analysis of multiple lymphoma tissues from one autopsy showed evidence that a single lymphoma clone was responsible for dissemination. The latent EBV nuclear antigen (EBNA- 1) transcripts detected in the HIV-related lymphomas were characteristic of the pattern found in Burkitt lymphoma (g1 EBNA1) and not in transplant-related lymphoproliferations. However, unlike Burkitt lymphoma, EBV latent membrane-associated protein (LMP) transcripts were also detected, thereby constituting an EBV expression pattern (g1 EBNA1+, LMP+) not previously observed in B-cell lymphomas. These findings demonstrate a high frequency of EBV-associated lymphomas in the setting of HIV infection that are distinct from the lymphoproliferations that arise during iatrogenic transplant-associated immuno-suppression or in the general population. However, it is also apparent that HIV-related lymphomas are biologically heterogeneous, which may reflect the multiple mechanisms or steps necessary for eventual malignant transformation.