This study compared the attitudes of 16 adolescents (8 males and 8 females) with cystic fibrosis (CF) toward exercise and physical activity (PA) before and after a 6-week exercise program. Although the boys and girls had similar ages (12-18 years), the boys were fitter and leaner and had higher pulmonary function. Subjects reported both positive exercise attitudes of self and perceived attitudes of parents/friends that remained essentially unchanged after strenuous training. Boys reported higher vigorous activities at baseline than girls, but all subjects increased participation in very hard PAs after training. Girls had small but nonsignificant increases in PA at each (mild-vigorous) level. Results emphasize that adolescents with a mild to moderate lung disease can significantly increase PA in a nursing intervention.