Lymphoproliferative disease (LPD) is a recognized complication of primary immunodeficiency (PID) and immunodysregulatory syndromes. Historically, it has a very poor outcome. For patients surviving LPD, myeloablative hematopoietic stem cell transplantation (SCT) was the only cure for the underlying PID, with a high risk of developing posttransplantation complications, including recurrent lymphoproliferative disease. We describe 8 patients with a range of PID and immunodysregulatory syndromes complicated by LPD. After initial treatment of the LPD (including the use of anti-CD20 monoclonal antibody, rituximab, in 6 of the patients), all patients underwent reduced-intensity conditioning (RIC) SCT with prospective monitoring for Epstein-Barr virus (EBV) viremia. After transplantation, 3 patients received rituximab, and 3 patients received prophylactic EBV-specific cytotoxic T-lymphocytes. Only 1 patient developed recurrent LPD posttransplantation, which responded to rituximab. All patients who underwent transplantation survive free of LPD and are cured of their PID at a median follow-up of 4 years (range, 1-7 years). With careful monitoring and pre-emptive therapy, we advocate this RIC SCT approach to patients with PID who have pre-existing EBV-LPD.