Intra-alveolar haemorrhages represent frequent and severe complications in acute leukaemia treated with chemotherapy. Thrombocytopenia with or without associated haemostasis disorder in association with infectious or toxic lesions of the alveolar membrane (related to radio- or chemotherapy) represent the major promoting factors. Presence of intra-alveolar haemorrhage is mainly suspected on X-ray chest roentgenogram and can be confirmed by bronchoalveolar fluid examination demonstrating an excess of siderophages. Prevention of this complication is based upon reduction of risk factors. Platelet transfusions and careful introduction of steroids are proposed in certain cases.