We report 4 pediatric cases of biopsy-proven posttransplant lymphoproliferative disorder (PTLD) in the context of allogeneic hematopoietic stem cell transplantation (HSCT). All cases showed diffuse staining with latent membrane protein-1 in immunohistochemistry. The median age at transplant of 4 patients with PTLD was 10.1 years (range, 2.2 to 13.2 y). The median interval between HSCT and the diagnosis of PTLD was 5.5 months (range, 4 to 8 mo). All patients were treated with rituximab at dosage of 375 mg/m at weekly intervals. Reduction of immunosuppression was warranted in all cases. All patients survived with median follow-up duration of 27 months. Although PTLD has been rare following allogeneic HSCT, reduction of immunosuppression combined with rituximab yielded significant response rates in patients with this infrequent but potentially lethal complication. The preliminary finding of this study demonstrated that severe aplastic anemia is closely associated with the development of PTLD in children.