We attempted to determine the responsiveness and validity of the Quality of Well-Being (QWB) scale in 20 consecutive children and adolescents with cystic fibrosis. The QWB score was determined for 6-day periods immediately before and after hospital admission, and at 6- and 12-month follow-up. With the instrument's scale of zero-1, responsiveness was indicated by significant changes in QWB score (0.09), physical (0.019), social (0.021), and symptom-problem complexes (0.04) domains, and all pulmonary function tests from before to after treatment of an acute exacerbation. Only the symptom-problem complex domain significantly changed from after treatment to 6- and 12-month follow-up. Validity was shown by significant correlations between before and after QWB scores and forced vital capacity (r=0.476), residual volume total lung capacity ratio (r=0.452), forced expiratory volume in 1 second (r=0.358), and forced expiratory flow between 25% and 75% of vital capacity (r=0.35).