Hemopoietic stem-cell transplant patients may require intensive blood component support. Complications of transfusions include transmission of viral and bacterial infections, transfusion-associated graft-versus-host disease and transfusion-related acute lung injury. Alloimmunization to red cell antigens may cause difficulties in selecting compatible blood, while alloimmunization to HLA expressed on platelets may cause subsequent platelet transfusion refractoriness. It is essential to define robust transfusion policies and procedures and these should be regularly audited. This article reviews blood component transfusion in the setting of hemopoietic stem-cell transplant and specifically discusses the management of ABO-mismatched transplants, the prevention of cytomegalovirus transmission, the prevention of transfusion-associated graft-versus-host disease and the use of granulocyte transfusions.