Computed tomography (CT) has been performed in 21 patients with primary hyperparathyroidism (HPT) in an attempt to localize preoperatively the parathyroid tumors. Eighteen of these patients also had ultrasound examinations. The CT examinations included the neck and mediastinum and were performed before and after contrast medium administration. At subsequent surgery, 24 enlarged glands were found, 20 in the neck and 4 in the mediastinum. In the neck, two were locally recurrent carcinomas. The true positive diagnostic rate for ultrasound was 60% with a false positive rate of 15% and a false negative rate of 25%. The CT examinations resulted in 70.9% true positive, 8.3% false positive, and 20.8% false negative diagnoses. The combination of both methods in the 18 patients so studied resulted in 80% true positive, 10% false positive, and 10% false negative findings. The CT examination procedure and its interpretation and limitations in primary HPT are described.