Acute lung injury (ALI ) and its more severe form, acute respiratory distress syndrome (ARDS ), are important critical care syndromes for which the treatment options are limited once the condition is fully established. Enormous basic and clinical research efforts have led to improvements in supportive treatment, but surprisingly little has been done on the prevention of this devastating syndrome. The development and progression of ALI /ARDS may be triggered by various intrahospital exposures including but not limited to transfusion, aspiration, mechanical ventilation, certain medications and delayed treatment of shock and infection. Early recognition of patients with or at risk of ALI /ARDS is essential for designing novel prevention and treatment strategies. Automated electronic screening tools and novel scoring systems applied at the time of hospital admission may facilitate enrollment of patients into mechanistic and outcome studies, as well as future ALI /ARDS prevention trials.