We reviewed 137 cases of hyperparathyroidism followed for 6-72 months to determine the reasons for failure and to outline the successful management of reoperative hyperparathyroidism. Of 127 patients treated initially at Thomas Jefferson University Hospital, three required reoperation (2.4%) and 10 were referred with recurrent or persistent hyperparathyroidism. Reasons for failure were a missed gland in eight cases (62%), an ectopic gland in two cases (15%), supernumerary glands in two cases (15%), and malignant degeneration of an autotransplant in one case (8%). One patient had shortterm hypoparathyroidism requiring vitamin D supplementation (5.6%), but there were no injuries to the recurrent laryngeal nerves. We conclude that adequate knowledge of the location of normal and ectopic glands with meticulous search will reduce most reoperations, and, with identification of all four glands and routine cervical thymectomy in multigland disease, the rate should be less than 5 per cent. Patients requiring reoperation should undergo noninvasive localization studies and, if equivocal, selective venous sampling for parathyroid hormone. The major complication rate should be less than 10 per cent.