PURPOSE: To determine the utility of HRCT in the diagnosis of chronic airflow obstruction and to correlate the morphologic abnormalities revealed by this modality with functional impairment in patients with chronic air-flow obstruction. MATERIALS AND METHODS:This study involved 80 patients with chronic airflow obstruction who underwent HRCT and a pulmonary function test. Final clinical diagnosis in these patients was determined by a chest physician on the basis of clinical features, bronchoscopy, pulmonary function test, and HRCT. In order to diagnose and determine the extent of areas of decreased attenuation revealed by HRCT (the CT score), the find-ings of HRCT were retrospectively reviewed by two radiologists, who reached a consensus. Clinical and HRCT diagnoses were then compared, and the rate of agreement between them was calculated. The relation-ship between the extent of areas of decreased attenuation revealed by HRCT and by FEV1/FVC was evaluated using Correl 's account and Student 's unpaired t-test. RESULTS: The agreement rate between clinical and HRCT diagnoses was 77.5% (62/80). The rates for bronchiec-tasis (88.9%, 24/27), emphysema (93.9%, 31/33), and bronchiolitis obliterans (100%, 6/6) were considerably higher than those for chronic bronchitis and bronchial asthma. The correlation rate between CT score and FEV1/FVC was significant in bronchiectasis (p<0.05; r: -0.76) and bronchiolitis obliterans (p<0.01; r:-0.66), but not in cases involving emphysema, bronchial asthma, or chronic bronchitis (p>0.05). CONCLUSION: HRCT is valuable in the diagnosis and prediction of physiologic impairment in patients with bronchiectasis and bronchiolitis obliterans, but has limited value in those with emphysema, chronic bronchitis or asthma.