The editorial in this issue of CHEST by Juniper1 stresses the importance of using only authorized versions of medical questionnaires that are designed to measure patients' subjective health status. Such questionnaires generally are referred to as patient-reported outcome (PRO) measures, and research on their development, validation, and cultural adaptation has grown into a field of study in its own right. The US Food and Drug Administration2 has defined a PRO as a measurement of any aspect of a patient's health status that comes directly from the patient (ie, without the interpretation of the patient's responses by a physician or anyone else). PRO measures can be used in a clinical trial or clinical setting to assess different aspects of patients' health status, including symptoms, functioning, health-related quality of life, and satisfaction with treatment. They can provide valuable information on how patients feel that would be difficult or impossible to obtain by conventional clinical measurements, particularly when different treatments have comparable effects with regard to disease control but different effects on health-related quality of life, or when changes in clinical measurements do not translate directly into recognizable patient benefit. Regulatory agencies increasingly recognize the importance of PRO measures, as illustrated by the US Food and Drug Administration draft guidance2 on the use of PRO measures in medical product development to support labeling claims and the European Medicines Agency3 reflection paper on the use of health-related quality-of-life measures in the evaluation of medicinal products.