A novel, short, and simple questionnaire, the Airways Questionnaire 20 (AQ20), has been developed to measure and quantify disturbances in the health-related quality of life (HRQoL) of patients with asthma or chronic obstructive pulmonary disease (COPD). The AQ20 has 20 items with yes/no responses, and should take 2 min to complete and score. The purpose of this study was to assess the discriminative properties and responsiveness of the AQ20 in patients with COPD. First, in a cross- sectional study, 165 patients with mild-to-severe COPD (mean age, 69 +/- 7 yr; FEV1, 40 +/- 16% of predicted) completed the AQ20, the St. George's Respiratory Questionnaire (SGRQ), the Chronic Respiratory Disease Questionnaire (CRQ), pulmonary function tests, a progressive cycle ergometer exercise test, and an assessment of their dyspnea and anxiety. The score distribution of the AQ20 was skewed toward the mild end of the scale, whereas the SGRQ and CRQ showed a normal distribution. The AQ20 showed a moderately strong correlation with the maximal oxygen uptake and the assessment of dyspnea (Spearman's correlation coefficients [rs] = -0.49, -0.60, respectively), but a weak correlation with the FEV1 (rs = -0.18). Moderate to strong correlations were also recognized between the AQ20 and SGRQ and CRQ (rs = -0.80, -0.72, respectively). Multiple regression analysis revealed that dyspnea and anxiety accounted for 43% of the variance in the AQ20, almost the same as in the SGRQ and CRQ. Second, longitudinal changes over time in the FEV1, AQ20, SGRQ, and CRQ were examined in 86 patients with newly detected COPD (mean age, 69 +/- 8 yr; FEV1, 45 +/- 19% of predicted). All three measures showed significant improvements in their scores over a 3-mo period after initiating medical intervention. The change in the AQ20 showed a moderate to strong correlation with each dimension of the SGRQ and CRQ (rs = 0.56, -0.52, respectively), but no significant correlation was noted with the FEV1. In conclusion, the AQ20 may have discriminative properties and responsiveness that are similar to more complex questionnaires such as the SGRQ and CRQ. Because it is short and can be quickly answered and scored, the AQ20 may be useful in studies with limited time for HRQoL assessments.