Cystic fibrosis (CF) is an inherited, chronic disease which mainly affects the lungs and the nutrition. Intensive treatment has gradually improved the outcome for the patients. Exercise therapy has been increasingly advocated to be included in the CF regimen. Our own studies indicate that both short-term and long-term training ameliorate the physical conditions for CF patients, that there is no danger for well-trained CF patients - both boys and girls - to take part even in vigorous, prolonged exercises, and that CF patients might have a positive attitude toward physical activities. Of course, all physical activities have to be individually designed. A review of the literature is also given: The specific ventilatory factors in CF, the limitations of exercise, the problem with exercise-induced asthma, the training effect on lung drainage, on lung function, on infections, on biochemical and hormonal variables, on nutrition and the gastrointestinal tract, on the musculoskeletal apparatus, and on the mind. Nearly all these reports are favorable for a carefully monitored, high activity in CF patients. Practical considerations for activities are given.