The occurrence of posttransplant lymphoproliferative disorder (PTLD) in solid organ allograft recipients can be quite varied in clinical presentation, histopathological characteristics and frequency. A variety of lymphomas can develop as a PTLD although some types appear infrequently and remain poorly understood in this clinical setting. In this report, we describe two cases of Burkitt s lymphoma presenting as a PTLD following liver transplantation. The recipients were 12 and 44 years of age and displayed gastrointestinal involvement by the tumors several years following transplant. The tumors displayed the typical histological features of Burkitt s lymphoma and were markedly positive for EBV. The tumors displayed similar immunophenotypic characteristics by flow cytometry and had rearrangements of the immunoglobulin J-H heavy chain. The tumors required aggressive chemotherapy and a cessation of immunosuppressive therapy. This report demonstrates that Burkitt s type lymphomas can develop in the posttransplant setting and that these tumors contain morphologic, cytofluorographic and molecular features identical to Burkitt s lymphomas that occur in non-transplant patients. Our experience is that these PTLD- Burkitt s lymphomas behave aggressively and require intensive chemotherapeutic intervention.