Hematopoietic stem cell transplantation (HSCT) may take place in the form of an autologous or allogeneic transplant depending on the indication for transplantation. Because of the myeloablative conditioning regimens preceding HSCT, deep thrombocytopenia is experienced by most of the stem cell recipients in whom replenishment of leukocytes and platelets is expected within the first month following the transplantation. Prolonged thrombocytopenia, on the other hand, usually develops as a delayed complication of allogeneic stem cell transplantation (allo-SCT) and is associated to the source of stem cells, quantity of the infused CD34+ cells, graft-versus-host-disease (GVHD), insufficient engraftment, relapse of the malignancy, microangiopathy, alloimmunisation, medications, or viral infections. In an attempt to explain pathogenesis leading to post-HSCT thrombocytopenia, two main theories have been proposed. First one is the peripheral destruction caused by anti-platelet antibodies, splenic sequestration, or other factors. The latter blames insufficient platelet generation due to impaired thrombopoiesis. Nevertheless, most of the clinical conditions arise with overlapping of both mechanisms.Here we present a pseudothrombocytopenia case induced by donor-related ethylene-diamine-tetra-acetic acid (EDTA) as an unanticipated cause of thrombocytopenia to which most recipients of allo-SCT are prone to.