Computed tomography (CT) of the neck and mediastinum was performed in 10 patients with primary hyperparathyroidism. Nine had undergone previous surgery and were considered localization problems. Of four subsequently proven cervical adenomas, only one unusually large 19-g adenoma was visualized by CT. However, of two subsequently proven anterior mediastinal adenomas, CT scanning was positive in both; a single posterior mediastinal adenoma was not demonstrated. Of the remaining three patients, one was not operated on; in two others no adenoma was found at surgery. CT scanning is recommended prior to neck surgery in all patients with primary hyperparathyroidism to identify adenomas in the anterior mediastinum.