For decades the incidence of the acute respiratory distress syndrome (ARDS) has been unclear. A first effort to tackle the problem was undertaken by the National Heart and Lung Task Force who, in 1972, provided the scientific community with an arguable estimate of 75 cases per 100,000 inhabitants/year for the USA. Nearly 20 years later, the first population based studies yielded figures of 1.5-4.5 cases per 100 000 inhabitants/year in Europe. Epidemiologic research became much more focused when in 1992 the new ARDS and acute lung injury (ALI) definitions of the American-European Consensus Conference became available. In subsequent studies in which these refined definitions were used, incidence figures ranging from 13-23 cases per 100,000 inhabitants/year for ARDS and 18 cases per 100,000 inhabitants/year for ALI were reported. Latest results from a high-class epidemiological study conducted in Seattle, suggested ARDS/ALI incidence figures of 59 and 79 cases per 100,000 inhabitants/year, respectively. These new figures, similar to the one proposed in 1972, led to a paradigm shift: ARDS and ALI are no longer viewed as rare syndromes but as widespread diseases with a massive socio-economic impact that is comparable with the burden from breast cancer, AIDS, asthma or myocardial infarction.