OBJECTIVES: To assess the measurement properties and response to change of the Spanish version of the CAT questionnaire during exacerbations of COPD (ECOPD). METHODS: Observational, prospective study in 49 centers in Spain. Patients hospitalized because of ECOPD (n=224) completed the CAT, the St. George’s Respiratory Questionnaire-adapted for COPD (SGRQ-C) and the London Chest Activities of Daily Living (LCADL) questionnaire during the first 48 hours of admission and 4±1 weeks after hospital discharge. Another group of clinically stable COPD patients (n=153) also completed the same questionnaires on two occasions, at recruitment and 4±1 weeks later. RESULTS: Internal consistency (Cronbach’s alpha) was 0.86. Test re-test reliability (Intraclass Correlation Coefficient) was 0.83. CAT scores correlated with both the SGRQ (r=0.82; p<0.01) and the LCADL (r=0.63; p<0.01). Change in CAT during ECOPD correlated well with change in SGRQ (r=0.63, p<0.01).The CAT discriminated between stable and ECOPD patients (15.8 vs 22.4, p <0.01), as well as between patients with different levels of airflow limitation and dyspnea (MRC scale). The effect size in CAT scores for ECOPD patients reporting their health state as “much better” after discharge was 0.90; for “quite a lot better” 0.63, and for “slightly better” 0.59. CONCLUSIONS: The Spanish version of CAT is sensitive to change during ECOPD and has similar properties to those of the original English version.  Funded by GlaxoSmithKline.