A 1-year survey of patients in three hospitals identified 936 patients who had one predisposition and 57 who had several predispositions to the adult respiratory distress syndrome. From the total predisposed population of 993 patients, 68 subsequently developed the syndrome. An additional 20 patients developed the syndrome from causes other than eight identified predispositions, to bring the total of patients studied to 88. A highly significant difference (p less than 0.0001) was found in the incidence rates of the syndrome between patients with one and several predispositions (5.8 versus 24.6 per 100 patients). Within 72 hours of onset of predisposition, 89.5% of patients who developed the syndrome had been intubated and placed on mechanical ventilation. Fifty-seven of the 88 patients (64.8%) with the syndrome died. By the 14th day 90% of deaths had occurred. There were no age- or sex-specific differences in either incidence or mortality rates. Case fatality rates of the syndrome were high in all predisposed groups.