Pulmonary complications of transfusion were once believed to be infrequent and relatively unimportant in terms of morbidity. Transfusion-related acute lung injury (TRALI) and transfusion-associated circulatory overload (TACO) are now appreciated as being relatively common and clinically important. TRALI is one of the two most frequent causes of transfusion-associated death and patients with TACO have longer hospitalizations and increased morbidity. Both entities are diagnosed primarily on clinical grounds but laboratory tests are available which can confirm or supplement the clinical impression. The high-risk patient for TRALI has not been identified but in TACO, very young or older patients who are transfused too rapidly or with too much volume are the most vulnerable. The mechanism of TRALI is incompletely understood but antibodies in stored blood components certainly play an important role. In TACO, the problem is primarily a mechanical issue. Prompt recognition is the key to successful treatment for both entities.