Transfusion-related acute lung injury (TRALI) is a serious condition characterized by respiratory distress, hypoxia, and bilateral pulmonary infiltrates, which occur within 6 hours of transfusion. Several theories have been proposed to explain the underlying pathologic mechanisms of TRALI. Immune-mediated TRALI accounts for over 80% of reported cases and is mediated by donor antibodies to HLAs and/or human neutrophil antigens (HNA). Immune-mediated TRALI is most commonly associated with donor plasma transfusion or other blood products from multiparous women, which has led many countries to reduce or exclude women from donating high-volume plasma products. This policy change has resulted in a decrease in the incidence of TRALI and highlighted the importance of nonimmune-mediated TRALI, which is thought to be caused by bioreactive lipids and other biologic response modifiers that accumulate during storage of blood products. When TRALI is suspected, clinical consultation with a transfusion medicine specialist helps differentiate it from other transfusion reactions with similar characteristics.