Cystic fibrosis is a chronic, multisystem genetic disease with a wide variability in clinical severity. In recent years, advances in therapy have led to improved patient survival into adulthood. New treatments are rapidly being developed and require evaluation to determine their efficacy. The measurement of health-related quality of life in cystic fibrosis provides additional information about the impact of this disease that cannot be obtained by physiological tests such as pulmonary function. An instrument to measure health-related quality of life is especially useful as an outcome measure for clinical trials. To date, only a few general quality-of-life (QOL) measures have been used in people with cystic fibrosis. There has been some demonstration of validity in 2 measures (the Quality of Well-Being Scale and the Functional Status Index) but the responsiveness of these instruments in this population has not been established. A cystic fibrosis-specific QOL instrument would be valuable as an outcome measure because of its potential for increased responsiveness, but no published measures exist as yet.