The public health burden of acute lung injury (ALI/ARDS) in terms of morbidity, mortality, length of hospitalisation, and need for rehabilitation is poorly appreciated. This study reports the results of a prospective, population based, cohort study conducted in 21 hospitals in and around King County, Washington, USA to determine the incidence and mortality associated with ALI/ARDS. Between April 1999 and July 2000, 4251 adults requiring mechanical ventilation for more than 24 hours were screened. Of the 1687 patients with acute hypoxaemic respiratory failure, 1113 had ALI, 828 of whom (74%) had ARDS. The crude incidence of ALI/ARDS was 78.9/58.7 cases per 100 000 person-years, respectively, giving age adjusted national estimates of 86.2/64 cases per 100 000. The in-hospital mortality was 38.5% for ALI and 41.1% for ARDS. Mortality increased with age, reaching 60% for patients aged 85 or older. The calculated incidence of ALI/ARDS in this study was 2–40 times higher than previously reported with an estimated 190 600 new cases of ALI every year requiring 3.6 million hospital days, 2.15 million ICU days, and leading to 74 500 deaths. This number is comparable to the deaths due to breast cancer or HIV in the USA in 1999. Of note, only 34% of the survivors were discharged directly home while 51% were transferred to rehabilitation or nursing facilities.

This study provides us with a better understanding of the epidemiology of ALI/ARDS which is useful for allocating future ICU resources and planning physical and neurocognitive rehabilitation programmes for ICU survivors.