Transfusion-Related Acute Lung Injury (TRALI) is a post-transfusion acute respiratory distress syndrome (ARDS). TRALI is a non-cardiogenic lung oedema occurring within 6 hours following the infusion of a blood component. Its frequency has been estimated from 1 in 5.000 to 1 in 500.000 injected blood products. Its aetiology is still controversial. Antibodies against HLA class I molecules or granulocyte surface molecules recognizing recipient leukocyte antigens were implicated at first. More recently anti HLA class II were involved in some cases. Finally granulocyte activating lipids released from cells during blood storage were claimed to account for cases in which no antibody were detected. Nevertheless, in most cases, none of these triggering factors alone seems sufficient to induce a TRALI. A predisposing condition, associated with leucostasis in pulmonary vessels, is required. Whatever the mechanism, the pulmonary lesion is eventually due to release of neutrophil granule content in contact with endothelial cells of lung micro-capillary vessels. The basement membrane damages leads to fluid and cell extravasations in interstitial and alveolar spaces. Among blood donors multiparous women are the most frequently involved. Up to now there are neither definite guidelines regarding detection of harmful antibodies nor regulation for deferral of potentially dangerous blood donors.