To determine the incidence and 28-d mortality rate for acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) using the 1994 American-European Consensus Conference definitions, we prospectively screened every admission to all 21 adult intensive care units in the States of South Australia, Western Australia, and Tasmania (total population older than 15 yr of age estimated as 2,941,137), between October 1 and November 30, 1999. A total of 1,977 admissions were screened of which 168 developed ALI and 148 developed ARDS, which represents a first incidence of 34 and 28 cases per 100,000 per annum, respectively. The respective 28-d mortality rates were 32% and 34%. The most common predisposing factors for ALI were nonpulmonary sepsis (31%) and pneumonia (28%). Although the incidences of ALI and ARDS are higher and the mortality rates are lower than those reported from studies in other countries, multicenter international studies are required to exclude methodological differences as the cause for this finding.