Cryptogenic organizing pneumonia (COP, formerly bronchiolitis obliterans organizing pneumonia) is rare in children. We describe an 11-year-old girl with Epstein-Barr virus (EBV) reactivation/presumed post-transplant lymphoproliferative disease (PTLD) 15 months after undergoing a deceased donor kidney transplantation. Treatment with reduced immunosuppression, ganciclovir, and cytomegalovirus immunoglobulin was complicated by severe graft rejection, prompting therapy with methylprednisolone, anti-thymocyte globulin and four weekly doses of rituximab (total 1500 mg/m(2)). Tacrolimus- and prednisone-based anti-rejection prophylaxis was complemented with low-dose sirolimus. When the lactate dehydrogenase and uric acid levels rose 10 weeks after the first rituximab infusion and bilateral pulmonary nodules were detected by computerized tomography, recurrence of PTLD was suspected. Open lung biopsy of the clinically asymptomatic patient identified the nodules as COP, characterized by abundant CD3(+) T-cells, few B-cells, and the absence of EBV, cytomegalovirus, or adenovirus antigens. With normalization of the peripheral B-cell count, EB viremia reappeared and persisted, despite minimal immunosuppression. Four years later, the patient was diagnosed with classical Hodgkin lymphoma-type PTLD with multiple pulmonary and abdominal nodes. This first report of rituximab-associated, pediatric COP highlights the risk of pulmonary complications after treatment with B-cell depleting agents in solid organ transplant recipients, and the importance of a histopathologic diagnosis and vigilant follow-up of such lesions.