Respiratory diseases in childhood can cause sequelae reaching far beyond childhood. The growing lung and airways are particularly sensitive to insults, including infection, inflammation, and allergic sensitization. There are many possible mechanisms that connect childhood respiratory illness to respiratory morbidity and mortality in the adult. The most important mechanisms are direct damage to the developing lung and airways, induction of bronchial hyperresponsiveness, chronic inflammation, and possibly chronic viral infections in the tissues of the respiratory system. The elucidation of childhood respiratory problems should be an integral part of the evaluation of adults with chronic respiratory disease.