Bronchiectasis is an irreversible bronchial dilation that may require surgery for successful treatment. Plain radiographic findings are usually not specific, and bronchography is often necessary for confirmation. We compared CT with bronchography to assess the utility of CT in diagnosing and determining the extent of bronchiectasis. Twenty-six bronchograms were performed in 14 patients. A segment-by-segment analysis of the presence, extent, and type of bronchiectasis was made. In 10 lungs, results of bronchography and CT were both negative, and in 10 other lungs results of CT and bronchography were both positive. In six lungs CT results were negative, but results of bronchography were positive. There were no false-positive CT diagnoses. In six of 10 lungs in which CT and bronchography demonstrated bronchiectasis the extent of disease was underestimated by CT. False-negative CT occurred when there were small foci of cystic bronchiectasis (minimal degrees of cylindrical bronchiectasis), or when pulmonary opacities obscured the bronchi. In three cases, thin section (1.5 mm) CT demonstrated improved definition of bronchi but did not alter the estimated extent of bronchiectasis. We conclude that, although in 77% (20/26) of the lungs CT correctly detected or excluded bronchiectasis, CT was less sensitive than bronchography and underestimated the number of diseased segments.