Transfusion-associated graft-versus-host disease (TGVHD) has been reported in 131 patients as a complication of supportive treatment with an overall 90% mortality. This study was undertaken to define the historical incidence of TGVHD, its symptomatology, and mortality among affected patients by age, diagnosis, and blood product transfused. Although the use of irradiated blood products (IBPs) virtually eliminates the risk of this highly lethal complication, the use of IBPs appears variable. To ascertain current use of IBPs, questionnaires were sent to 100 pediatric and adult hematologists, oncologists, and bone marrow transplant physicians asking their perceptions about and actual use of IBPs. The results of the questionnaire, information on irradiation effects on cellular blood products, and current recommendations for irradiation of blood products are discussed.