Although recognition of the importance of educating chronic obstructive pulmonary disease (COPD) patients has grown in recent years, their understanding of this disease is not being measured due to a lack of specific instruments. The aim of this study was to validate the COPD-Q questionnaire, a 13-item instrument for determining COPD knowledge.The COPD-Q was translated and backtranslated, and subsequently submitted to logic and content validation by a group of COPD experts and 8 COPD patients. Reliability was studied in an independent group of 59 patients with severe COPD seen in the pulmonology ward or clinics of 6 hospitals in Spain (Andalusia, Baleares, Castilla-La Mancha, Galicia and Madrid). This sample was also used for other internal and external validations.The mean age of the group was approximately 70 years and their health awareness was low-to-medium. The number of correct answers was 8.3 (standard deviation: 1.9), median 8, range 3-13. Floor and ceiling effects were 0% and 1.5%, respectively. Internal consistency of the questionnaire was good (Cronbach's alpha=0.85) and reliability was also high, with a kappa coefficient >0.6 for all items and an intraclass correlation efficient of 0.84 for the total score.The 13-item COPD-Q is a valid, applicable and reliable instrument for determining patients' knowledge of COPD.