The inclusion of health-related quality of life (HRQoL) as an outcome measure in cystic fibrosis (CF) clinical trials can supply important patient-reported information not captured by other endpoints. Both an appropriate HRQoL measure and sound methodology are required in order to draw valid inferences about treatments and HRQoL. This paper provides the current consensus of the HRQoL Outcomes Group. Particular consideration has been given to the appropriateness of measurement scales, the rationale for including specific domains as endpoints, the importance of considering baseline ceiling effects and the difficulties of data interpretation. Guidance is provided on HRQoL measurement in National and European CF clinical trials.