Background. Allogeneic hematopoietic stem cell transplantation recipients have an increasing risk of both hemorrhagic and thrombotic complications. However, the competing risks of two these life-threatening complications in these complex patients are currently not well defined. Design and Methods. We retrospectively analyzed data from 431 allogeneic transplantation recipients to identify the incidence, risk factors and mortality due to thrombosis and bleeding. Results. Significant clinical bleeding was more frequent than symptomatic thrombosis. The cumulative incidence of a bleeding episode was 30.2% at 14 years. The cumulative incidence of a venous or arterial thrombosis at 14 years was 11.8% and 4.1%, respectively. The analysis of competing factors for venous thrombosis revealed extensive chronic graft versus host disease to be the only independent prognostic risk factor. By contrast, eight factors were associated with an increased risk of bleeding; advanced disease, ablative conditioning regimen, umbilical cord blood transplantation, anticoagulation, acute III - IV graft versus host disease and transplant-associated microangiopathy. The development of thrombosis did not significantly affect overall survival (p = 0.856). However, significant clinical bleeding was associated with inferior survival (p < 0.001). Conclusions. In allogeneic hematopoietic stem cell transplantation, significant clinical bleeding is more common than thrombotic complications and affects survival.