Exercise is an important aspect of health and development in children. By placing the pulmonary system under stress, exercise testing may reveal subtle dynamic abnormalities that are not apparent on conventional static pulmonary function tests. Furthermore, exercise testing assesses the functional impact of respiratory disease on children. Exercise testing has been used in children with a variety of respiratory diseases such as exercise induced bronchoconstriction, asthma, cystic fibrosis and bronchopulmonary dysplasia to assess the severity of disease as well as response to various interventions. Furthermore, there is good evidence that exercise testing is a useful tool to help determine prognosis in patients with cystic fibrosis. In addition to the clinical utility, exercise testing is also becoming an increasingly important outcome measure in research studies.