Transfusion-associated graft-versus-host disease (TA-GVHD) is a rare but fatal potential complication of transfusions. It is mediated by immunocompetent donor lymphocytes that cannot be eliminated by the recipient. Patients at risk for developing TA-GVHD are those who have a profound deficiency in cell-mediated immunity or those who share histocompatibility antigens with the donor and do not recognize the donor cells as foreign. Irradiation of cellular blood components is currently the only acceptable method for prevention of TA-GVHD. This practice guideline identifies the patient population who should receive irradiated blood components and describes the technical aspects of blood component irradiation that may affect the safety of the final product.