Post-transplant lymphoproliferative disorders (PTLDs) occur in 3.5-9% of patients after pediatric cardiac transplantation. Caution is needed when treating patients with PTLD because of the risk of allograft rejection frequently caused by withdrawal of immunosuppression. In this report, we describe a 47-month-old boy who developed PTLD as an ileocecal mass 29 months after cardiac transplantation. Immunosuppressive therapy with cyclosporine A (CyA) had been reduced due to an elevation of Epstein-Barr virus (EBV) titer for 8 months before development of PTLD. Histology of the tumor was diffuse large B cell lymphoma. EBV was detected by in situ hybridization assay. Cytogenetic analysis revealed t(8;14)(q24;q32) and Southern blot analysis detected a c-Myc rearrangement. He was treated with rituximab and combination chemotherapy with excellent response. CyA dose was maintained at reduced levels during chemotherapy and later minimized with introduction of everolimus. The child is free of both PTLD and allograft rejection 41 months after the diagnosis of PTLD.