Physical training in patients with pulmonary diseases, including cystic fibrosis (CF), may improve exercise tolerance in these patients. Most training programs are performed in a clinical setting. Little information is available concerning the effect of home exercise training programs in CF patients. The purpose of this study was to investigate the effect of a home exercise training program in CF patients. Ten adolescent patients (seven male and three female) with CF, mean (SD) age 20.6 (6.5) years, participated in a home exercise training program for 3 months. Pretraining condition was assessed during a control period of 2 months in which patients were asked to continue their normal daily activities. Home exercise training consisted of cycle training of 15 min at a submaximal workload once a day and was supervised by a physiotherapist two times a week. A follow-up period of 1 month, in which the patients were advised to continue cycling at home without supervision, was included after the training program. Pulmonary function, bicycle exercise test performance, and the degree of limitation in activities of daily living (ADL) were measured. No significant differences were found between the two pretraining assessments. After the training period we found significant improvement in maximal exercise capacity (Wmax) (mean [SEM]: 126  W before and 146  W after; p = 0.004), maximal oxygen uptake (VO2max) (mean [SEM]: 31.4 [2.1] ml.kg-1.min-1 before and 36.5 [2.5] ml.kg-1.min-1 after; p = 0.008), oxygen pulse (VO2/HR) (mean [SEM]: 10.9 [0.66] ml before and 11.9 [0.74] ml after; p = 0.047), and degree of limitation in ADL (mean [SEM]: 2.4 [0.43] before and 1.5 [0.48] after; p = 0.019) as compared with the initial values. Since no significant differences were found between the posttraining values and the results at the end of the follow-up period, the patients were apparently able to maintain the training effects during the follow-up period. We conclude that in CF patients, a home exercise training program, after clinical assessment of exercise tolerance, is an effective and relatively simple treatment to improve physical performance and decrease limitation in ADL and should be included in the maintenance treatment in these patients.