Transfusion reactions remain a common complication of transfusion therapy; reactions affecting the lungs are some of the most serious. Several different mechanisms are responsible for pulmonary transfusion reactions, and most cause adverse effects in addition to lung injury. Fluid overload can lead to pulmonary edema, antibodies reacting with plasma proteins can cause bronchospasm and anaphylaxis, and particulate matter can produce microemboli. These reactions are well understood and usually can be prevented. Transfusions are also associated with acute lung injury and acute respiratory distress syndrome (ARDS), but their etiology is poorly understood and they remain clinically problematic. Neutrophil antibodies cause some of these serious as well as mild pulmonary reactions, but the exact role of leukocyte antibodies in pulmonary reactions remains unclear. Other blood donor, blood component, and transfusion recipient factors likely play a contributing or modulating role in pulmonary transfusion reactions, but prospective studies are needed to better understand their role.