| INTRODUC TI ONPTLD is a significant cause of morbidity and mortality after allogeneic HSCT, mainly caused by EBV infection. It usually develops within few months after HSCT when cellular immune response is lacking so cytotoxic T cells are not able to control B cells harboring EBV. In the early course of PTLD, lymphoid proliferation is polyclonal; however, monoclonal diseases, such as high-grade lymphomas, can also develop. PTLD typically presents as a disseminated disease with fever, lymphadenopathy, and hepatitis. PTLDs most often involve lymphoid tissues, but extralymphatic involvement may occur as well.Primary CNS PTLD is an extremely rare condition following HSCT. The few case reports reveal difficulties both in diagnosis and therapy and confirm very poor prognosis. Effective strategy against EBV infection in the HSCT setting is based on weekly quantitative PCR scanning and timely introduced pre-emptive therapy. Treatment options for PTLD are reduction in immunosuppressive therapy, rituximab, cytotoxic EBV-specific T-cell infusion, and donor lymphocyte infusion. After failure of the abovementioned treatment modalities, systemic chemotherapy with or Abstract Primary CNS PTLD is an extremely rare complication after allogeneic HSCT. At our centre, an 11-year-old patient developed nausea, vomiting, and diplopy on day +82 following HSCT. On brain MRI, multiple white matter lesions were seen. Histology showed a diffuse large B-cell lymphoma with high load of EBV in tissue. Despite stopping immunosuppression, treatment with EBV-specific cytotoxic T cells, systemic rituximab, HD-MTX, and intrathecal chemotherapy, progression was observed. With a combination of HD-MTX and cytarabine, only a partial response could be achieved.