Transplantation of solid organs and haematopoietic stem cells requires immunosuppressive drug therapy in order to prevent rejection or graft-versus-host disease. Depending on dosage and type of drug, the risk of developing an Epstein-Barr virus (EBV)-associated post-transplant lymphoproliferative disease (PTLD) is increased. The lesion spectrum ranges from hyperplastic lesions to manifest lymphomas, the latter being classified as monomorphic PTLD. Hyperplastic changes, which are not distinguishable from viral reactions, comprise early or mononucleosis-like lesions. Those with effaced lymph node architecture or extranodal manifestation without a lymphoma-like phenotype are designated polymorphic PTLD. Monomorphic PTLD are either high grade B cell lymphomas, plasma cell neoplasms or Hodgkin lymphomas and only very rarely T cell lymphomas. Low grade B cell lymphomas do not occur. In a subfraction of cases, including even monomorphic PTLD, reduction of immunosuppression alone is sufficient to induce remission of the pathological process.