Transfusion-associated graft-versus-host disease (TA-GVHD) is rare but usually fatal complication of transfusion of any blood component containing viable T lymphocytes. TA-GVHD manifests as an acute syndrome characterized by the dysfunction of the skin, liver, gastrointestinal tract and bone marrow. The development of bone marrow aplasia increases the risk for hemorrhage and infection and most patients die within 1 month of transfusion. The risk associated with an individual transfusion depends on the number and viability of contaminated lymphocytes, the susceptibility of the patient's immune system to their engraftment and the degree of disparity in histocompatibility antigens between the donor and the patient. The risk of TA-GVHD are highest in recipients with immunodeficiency or immunosuppression. Prevention of TA-GVHD is of great importance as it cannot be treated successfully. Patients at risk must be identified and transfused with irradiated cellular blood products, as gamma irradiation inhibits the proliferation of donor lymphocytes and is currently the only recommended method for TA-GVHD prevention.