Epstein-Barr virus-associated B-cell lymphoproliferations are a serious complication of organ or bone marrow transplantation whose incidence is strongly influenced by a number of risk factors. The disease represents a model of Epstein-Barr virus-driven lymphoid neoplasia in the setting of immunodeficiency. The incidence and pathogenesis of posttransplant lymphoproliferations are examined in relation to the nature of the transplanted organ, the Epstein-Barr virus infection, and the use of specific immunosuppressive regimens. Pathologic classifications and molecular mechanisms for neoplasia are reviewed. Clinical manifestations, pathologic features, and diagnostic considerations are summarized, with emphasis on those aspects that differ significantly from classic non-Hodgkin's lymphoma. Existing data regarding treatment are reviewed, including reduction in immunosuppression, surgery, radiation, chemotherapy, interferon-alpha, monoclonal anti-B-cell antibodies, and T-cell therapy. A basis for the selection of therapeutic options is suggested.