A need was identified for a fixed-format self-complete questionnaire for measuring health in chronic airflow limitation. A 76-item questionnaire was developed, the St. George's Respiratory Questionnaire (SGRQ). Three component scores were calculated: symptoms, activity, and impacts (on daily life), and a total score. Three studies were performed. (1) Repeatability was tested over 2 wk in 40 stable asthmatic patients and 20 patients with stable COPD. The coefficient of variation for the SGRQ total score was 19%. (2) SGRQ scores were compared with spirometry, 6-min walking distance (6-MWD), MRC respiratory symptoms questionnaire, anxiety, depression, and general health measured using the Sickness Impact Profile score. A total of 141 patients were studied, mean age 63 yr (range 31 to 75) and prebronchodilator FEV1, 47% (range 11 to 114%). SGRQ scores correlated with appropriate comparison measures. For example, symptom score versus frequency of wheeze, r2 = 0.32, p less than 0.0001; activity versus 6-MWD, r2 = 0.50, p less than 0.0001; impact versus anxiety, r2 = 0.38, p less than 0.0001. Multivariate analysis demonstrated that SGRQ scores summed a number of areas of disease activity. (3) Changes in SGRQ scores and other measures were studied over 1 yr in 133 patients. Significant correlations were found between changes in SGRQ scores and the comparison measures (minimum r2 greater than 0.05, p less than 0.01). Multivariate analysis showed that change in total SGRQ score summed changes in a number of aspects of disease activity. We conclude that the SGRQ is a valid measure of impaired health in diseases of chronic airflow limitation that is repeatable and sensitive.