Computed tomography (CT) is used to detect emphysematous changes in the lungs of living patients. It is therefore important to develop a standard method for the radiographic quantification of emphysematous lesions using CT. The authors determine the best CT scanning methods for assessing the degree of pulmonary emphysema. Computed tomography scanning was performed in 85 consecutive patients with stable chronic obstructive pulmonary disease. Scans were obtained using 2-mm or 5-mm collimation, at full inspiration or full expiration, and with standard or high spatial-resolution reconstruction images (eight images each). Emphysema was then assessed by visual scoring using a five-point scale for each lung. Emphysema was scored as significantly less severe using standard reconstruction images. There were no significant differences in CT-scored emphysema on scans obtained with 2-mm and 5-mm collimation. Emphysema was scored as significantly less severe on expiratory scans. The postbronchodilator forced expiratory volume in one second value correlated better with emphysema scored on expiratory scans. Computed tomography-scored emphysema obtained by all methods correlated well with the diffusion capacity and total lung capacity, regardless of the method used. Using a visual scoring system with a five-point scale, narrow collimation is probably not necessary for the quantification of emphysema, although a high spatial-resolution reconstruction appears to be of value. Scans obtained in exhalation appear to underemphasize the severity of emphysema.