Management of monoclonal lymphoproliferative disease following stem cell transplantation is difficult and previous attempts to eradicate tumor using chemotherapy or radiation therapy alone have not been successful. We report successful early eradication of an EBV negative, B cell non-Hodgkin's lymphoma in a child who received a T cell-depleted, maternal haploidentical bone marrow transplant for severe combined immunodeficiency disease. Our treatment strategy involved combining conventional induction chemotherapy with re-transplantation using the paternal donor as a source of peripheral blood stem cells, followed by treatment with anti-CD 20 monoclonal antibody (Rituximab). This strategy exploits the potential graft-versus-tumor activity of the mature T cells in the graft, while providing a source of stem cells to confer long-term immune function. The administration of Rituximab in the early post-transplant course may provide additional anti-tumor activity without affecting the new stem cell compartment.