A study was undertaken to define the computed tomographic (CT) appearance of the lungs in subjects with uncomplicated asthma and to compare the prevalence of bronchial dilatation at CT in asthmatic and healthy subjects. Clinical features, pulmonary physiologic findings, chest radiographs, and high-resolution CT scans of 48 asthmatic subjects were reviewed. Forty-one (85%) of the 48 asthmatic subjects were undergoing bronchodilator therapy, 28 (58%) were undergoing steroid therapy, and 21 (44%) were cigarette smokers. Twenty-seven healthy control subjects underwent limited high-resolution CT. At selected CT levels, any bronchus with an internal diameter greater than that of the accompanying pulmonary artery was considered dilated. In the asthmatic subjects, 153 (36%) of 429 bronchi evaluated met criteria for bronchial dilatation compared with 37 (26%) of 142 bronchi in the control group (P < .05). Because bronchial dilatation demonstrated at CT did not correlate with clinical data, the authors conclude a bronchus larger in diameter than the adjacent vessel is not sufficient evidence to diagnose cylindric bronchiectasis.