Several studies have suggested that acute respiratory illnesses (ARI) may be precursors to chronic obstructive lung diseases, as well as being exacerbations of such diseases. The relationship of retrospective and prospective data on ARI to the prevalence and incidence of obstructive lung disorders has been examined in the community epidemiologic study of obstructive diseases a longitudinal study in Tucson. It has been determined that both the previous and subsequent history of ARI are significantly associated with the prevalence and incidence of airways obstructive diseases, those diagnosed by physicians and those inferred by symptoms. Lung function impairment also appears to be associated with such illnesses. This study implicates ARI as one of the major factors associated with the etiology as well as the natural history of chronic obstructive lung disease.