Airway development is only one of the factors that is important in the pathogenesis of complex respiratory disorders such as asthma and chronic airflow limitation. For example, knowledge of the interactions between the developing lung, genetic, environmental, and immunological factors is essential if progress is to be made in early diagnosis and the development of new interventions aimed at reducing the long term morbidity from chronic lung diseases. However, such a review is beyond the scope of this article which is limited to the role of airway development during childhood in determining adult lung function and the outcome of chronic airway disease. Some childhood respiratory diseases such as cystic fibrosis and various congenital lung disorders have obvious sequelae or adverse outcomes in adults. However, these conditions are relatively rare compared with chronic airflow limitation and asthma, the major symptomatic manifestations in adults of airway abnormalities. Most studies that have examined the aetiology of chronic airflow limitation and asthma have focused on airway calibre and bronchial responsiveness as possible pathophysiological factors and also as outcome measures with regard to the long term effects of chronic airway disease. This review will therefore focus on studies that have measured airway function including, in some studies, assessment of bronchial responsiveness.