We used technetium Tc 99m sestamibi for successful preoperative localization of abnormal parathyroid glands in nine patients with hyperparathyroidism and a history of neck surgery. The intraoperative and pathological findings were correlated with the preoperative technetium-sestamibi scan results. These nine patients had had 13 previous neck operations, two for thyroid disease, and 11 for hyperparathyroidism. In the two operated on for thyroid disease, the 99mTc-sestamibi scan localized a parathyroid adenoma. In one patient, the three remaining hyperplastic parathyroid glands were localized using 99mTc-sestamibi scan. The other six patients had 10 operations for hyperparathyroidism; the 99mTc-sestamibi scan localized the remaining parathyroid glands causing hypercalcemia. In this preliminary experience, the 99mTc-sestamibi scan localized all the abnormal parathyroid glands causing hyperparathyroidism in patients who had previously had neck surgery.