Fatal problems encountered in allogeneic stem cell transplantation include EBV reactivation and post transplant lymphoproliferative disorders (PTLDs) with high mortality rates. We performed a retrospective analysis in all consecutive adult and pediatric EBV reactivations and PTLD during a period of 8.5 years. There were 26 patients with EBV reactivation/PTLD out of a total of 854 transplantations giving an overall incidence of 3.0%. Specifically, the incidence of EBV-PTLD was 1.3%, whereas that of EBV reactivation was 1.8%. Median age was 46.0 and 11.0 years in the adult and pediatric patients, respectively. There were high rates (54%) of concomitant bacterial, viral, fungal and parasitic infections at the time of EBV manifestation. Variable treatment regimens were applied including in most cases an anti-CD20 regimen often in combination with virustatic compounds, polychemotherapy or donor lymphocytes. The mortality rates were 9 of 11 (82%) in patients with EBV-PTLD and 10 of 15 (67%) in patients with reactivation. Only 7 of 26 patients (27%) are alive after a median follow-up of 758 days (range 24-2751). The high mortality rates of EBV reactivation and of EBV-PTLD irrespective of multimodal treatment approaches emphasize standardization and optimization of post transplant surveillance and treatment strategies to improve control of these often fatal complications.