Posttransplantation lymphoproliferative disorders (PTLD) is not uncommon and can occur in 2% to 5% of solid organ recipients on immunosuppression. Epstein-Barr virus (EBV) infection or reactivation and intensive anti-T lymphocyte treatment are important pathogenetic factors for a large proportion of these disorders. Nonclonal lesions with polymorphous histology have a potential for regressing when the immunosuppressants are reduced or stopped. Clonal tumors with a monomorphous histology carry a poor prognosis, and the mortality rate for monoclonal lymphoma has been reported as high as 80%. We report a renal transplant recipient who developed high-grade monoclonal lymphoma only 4 months after a live-donor transplantation. The tumor was EBV positive. Reduction of immunosuppressants resulted in minimal regression of the tumor. The patient was treated with adoptive immunotherapy using ex vivo generation of autologous lymphocyte activated killer (LAK) cells. She had leukapheresis, and autologous peripheral blood mononuclear cells were obtained and cultured in interleukin-2 (IL-2)-rich medium for 9 to 10 days. The IL-2-activated LAK cells were reinfused into the patient without any systemic administration of IL-2. The patient experienced no side effects during the infusion. There was no rejection episode, and the renal function of the patient remained stable after treatment. Computed tomography scan performed 2 months after the infusion showed marked regression of the lesions in the liver and spleen. Five months later, magnetic resonance imaging showed complete resolution of the tumor lesions. Ultrasonography 13 months after the LAK cell infusion showed no lesion. The allograft function was not affected after treatment. Adoptive immunotherapy using IL-2-activated autologous LAK cells was effective in treating this renal transplant patient with EBV-positive high-grade lymphoma. The patient's kidney allograft functioned well without any rejection.