The Tucson Children's Respiratory Study (TCRS), begun in 1980, has followed 1246 subjects from birth together with their family members to delineate the complex interrelationships between a large number of potential risk factors, acute lower respiratory tract illnesses, and chronic lung disorders later in childhood and early adult life, especially asthma. Nine hundred seventy-four (78%) of the original subjects are still being followed. Among its numerous findings, the TCRS has (1) described various wheezing disorders (transient, nonatopic, atopic) and their characteristics; (2) developed an Asthma Predictive Index; (3) delineated the respiratory and atopic outcomes for children who had respiratory syncytial virus-related wheezing illnesses in infancy; and (4) evaluated a large number of risk factors for acute respiratory tract illnesses during the first 3 years of life. Future TCRS studies will focus on (1) factors in infancy and early childhood that relate to persistent asthma and atopy; (2) role of genetic factors in persistent asthma; and (3) determinants of lung function decline in early adult life.