Heart-lung transplant recipients are predisposed to acute rejection episodes, bronchiolitis obliterans, and opportunistic infections. In 9.4% of recipients at the University of Pittsburgh, a posttransplant lymphoproliferative disorder (PTLD) developed, and in 60% of cases, it presented in the allografted lungs and was associated with primary infection by Epstein-Barr virus (EBV). The PTLD is histologically indistinguishable from a primary pulmonary lymphoma and consists of a mixed population of large lymphoid cells, immunoblasts, and plasma cells. Two cases of PTLD were monoclonal with immunohistochemical and Southern blot analysis. Despite this, there was clinical recovery with reduced immunosuppression and acyclovir. We discuss the role of EBV in the development of PTLD and the pathogenesis of primary presentation in the allograft.