Transfusion-associated graft-versus-host disease (TA-GVHD) is a rare complication of blood transfusion. The disease is fulminant and fatal in most patients. TA-GVHD is caused by transfused alloreactive donor T lymphocytes that attack host tissue, including skin, liver, gastrointestinal tract and bone marrow. Most patients are immunocompromised, but immunocompetent patients can also be involved. Irradiation of blood components is generally recommended to prevent the onset of TA-GVHD for susceptible recipients. This review focus on pathogenesis and prevention of TA-GVHD.