Most monomorphic posttransplantation lymphoproliferative disorders (PTLDs) resemble diffuse large B-cell lymphoma or Burkitt lymphoma. Rare cases of PTLD resembling extramedullary plasmacytomas have also been described. This report describes the clinical, histologic, phenotypic, and genotypic findings in 4 cases of plasmacytoma-like PTLD (2 nodal, 1 adenoidal, and 1 cutaneous) and compares the findings with extramedullary involvement by plasma cell neoplasms arising in immunocompetent patients. Plasmacytoma-like PTLDs characteristically arise late after transplantation (mean, 7.0 years), show a variable association with Epstein-Barr virus (2/4 cases positive), and demonstrate histologic and phenotypic findings that overlap with immunocompetent extramedullary plasma cell neoplasms. None of the patients with plasmacytoma-like PTLD developed lytic bone lesions, and 3 of 4 patients had complete responses (>2 years) to reduction of immunosuppression, confirming the role of immunosuppression in the pathogenesis of these lesions. This report, which represents the first case series of plasmacytoma-like PTLD, clarifies the features of this rare subtype of PTLD.