The Tucson Epidemiological Study of Airway Obstructive Disease is a population-based prospective cohort study initiated in 1972 in Tucson, Arizona. At study initiation, 3,805 Tucson residents between the ages of 6 to 95 years participated. Due to study participants getting married and having children of their own, participation in the study ultimately increased to 5,377 people. The purpose of this study is to determine the natural history, etiology, and interrelationships of emphysema, chronic bronchitis, asthma, and related airways obstructive diseases. Also, to determine the relationship of acute lower respiratory tract illnesses in infants and children to the development of subsequent chronic lung disorders.