Posttransplant lymphoproliferative disorder is a rare but well-known complication in solid organ or hematopoietic transplant recipients secondary to immunosuppression. It can range from a cellular hyperplasia to a classic lymphoma. We describe a case of a nine-year-old male with Barth syndrome and a history of cardiac transplantation who developed plasmacytoid EBV-negative PTLD, an extremely rare entity in the pediatric population, and the evolvement of his PTLD to a more aggressive plasma cell neoplasm.