One hundred thirty-six patients meeting our criteria for one or more of eight clinical conditions were prospectively observed for the development of the adult respiratory distress syndrome. A high risk population was identified, including those with sepsis syndrome (38 percent), documented aspiration of gastric contents (30 percent), multiple emergency transfusions (24 percent), and pulmonary contusion (17 percent). The risk from multiple major fractures appeared low but contributed to the risk from other factors. The risk associated with just one factor (25 percent) was compounded by the presence of two (42 percent) and three (85 percent) simultaneous factors, and this finding was more predictive of ARDS than the injury severity score or initial arterial oxygenation. Of the ARDS cases, 76 percent occurred in the initial 24 hours after meeting the criteria. ARDS did not occur after 72 hours unless there was late development of sepsis (3 of 136 patients).