Computed tomography (CT) has been shown to detect both adrenal glands in 88.5% of upper abdominal examinations and can visualize at least one gland in 96.5% of patients. However, in examinations carried out specifically to visualize the adrenals, the glands were located in 98% of cases. This technique was used in 18 patients with primary aldosteronism to localize aldosterone-secreting adrenal tumours and to distinguish these from non-adenomas (bilateral adrenal hyperplasia). The results were compared with quadric analysis, a statistical technique used to predict the likely surgical outcome. In seven patients the CT results were verified by operation (six adenomas, one adrenal hypertrophy). However, in one further patient a large adenoma (20 mm in diameter) which had not been predicted by CT scanning was found at operation. In the remaining ten patients who have been medically treated, results concordant with quadric analysis were obtained in eight cases. We would suggest that CT scanning should be the initial investigation for the pre-operative localization of adenomas but further comparative studies are required.