OBJECTIVES: To assess the reliability of the quality of life instrument used in the COURAGE trial. METHODS: We used data from the COURAGE study, a randomized trial evaluating the outcomes of optimal medical therapy (OMT) with or without percutaneous coronary intervention (PCI).  A total of 2,287 patients with stable Coronary disease were enrolled and followed for a median of 4.6 years.  Angina-specific health status was assessed with the Seattle Angina Questionnaire (SAQ) at baseline and at 1, 3, 6 and 12 months followed by annual evaluations.  The SAQ consists of five domains:  the physical limitation, angina stability, angina frequency, treatment satisfaction, and quality of life. Scores in each domain range from 0 to 100, with higher scores indicating better health status.  Cronbach’s alpha was used to estimate the reliability of each domain in SAQ. RESULTS: At baseline, the correlation coefficients between the domain of physical limitation, angina frequency, or quality of life and the composite score of all five domains were 0.54, 0.63, and 0.65, respectively; but the coefficients between the angina stability or treatment satisfaction and the composite score were 0.49, and 0.27, respectively. If the domain of physical limitation, angina frequency, or quality of life is deleted, Cronbach’s alpha will decrease from 0.75 to 0.69, 0.66, or 0.64, respectively; however, if the angina stability is deleted, Cronbach’s alpha will change from 0.75 to 0.72, and if the treatment satisfaction is deleted,   Cronbach’s alpha will increase from 0.75 to 0.78.  Similar results can be seen over the follow-up time.  CONCLUSIONS: The angina stability and treatment satisfaction domains should be excluded since they had weak relationship with the entire SAQ instrument.  Three domains of the physical limitation, angina frequency, and quality of life thoroughly reflected the impact of angina on a patient’s health status and disease related quality of life.