Alpha-1-antitrypsin (AAT) deficiency is an inherited disorder associated with an increased prevalence of pulmonary emphysema. To date there has been no description of the appearances on CT of the emphysema associated with AAT deficiency. We have reviewed the CT scans of 17 patients with proven AAT deficiency. Eleven out of 17 were examined with HRCT. The CT features were correlated with those on chest radiography. Areas of low density corresponding to parenchymal destruction and reduced perfusion, and attenuation of the pulmonary vasculature were present in all cases. Frank bulla formation occurred in 7/17 patients and was not a major feature. A striking CT finding was bronchial wall thickening and/or dilatation in 7/17 patients with gross cystic bronchiectasis in one patient. In contrast to appearances on chest radiography the upper zones were affected in all cases (17/17) and fine section scanning was particularly valuable in demonstrating changes in these less severely affected regions. Estimation of the extent of disease correlated well with abnormal lung function tests.