SummaryExercise testing can be performed safely in cystic fibrosis patients, and provides a simple and reproducible index of overall health in the disease. A wide variability in exercise capacity of cystic fibrosis patients is found, but, in general, exercise is limited by the degree of lung disease and, to a lesser extent, by compromised nutritional status. Based on the results of exercise tests, patients can then be supplied with individualised exercise prescriptions. Exercise training can be expected to improve the exercise capacity of the majority of cystic fibrosis patients, but pulmonary function generally remains unchanged. Whether exercise rehabilitation will improve the long term prognosis for patients with cystic fibrosis is currently not known.