A study was performed to determine the value of computed tomography (CT) in the diagnosis and assessment of cylindrical and mild varicose bronchiectasis. Fifteen patients, in whom bronchography had shown such bronchiectasis in 34 of 73 lobes that could be assessed, were examined by CT. A control group of 12 subjects in whom there was no clinical or plain radiographic suspicion of bronchiectasis was also studied. Computed tomography (CT) was considered to show bronchiectasis in 28 lobes, 27 of which were bronchiectatic as shown by bronchography. Of 45 lobes where CT was not thought to show bronchiectasis, bronchography demonstrated 38 normal and seven bronchiectatic lobes. All lobes in the control group were interpreted as normal. Using bronchography as the definitive investigation for cylindrical or mild varicose bronchiectasis, CT has a sensitivity of 79% and a specificity of 99% in the diagnosis of the disease. The high specificity indicates that a diagnosis of cylindrical or mild varicose bronchiectasis by CT is reliable but CT is too insensitive to be used as a screening test.