A retrospective analysis of 93 patients undergoing 128 re-explorations for persistent or recurrent hypercalcaemia is presented. Seventy-six patients (82 per cent) became normocalcaemic after between one and five reoperations. Nine patients had hypercalcaemia caused by sarcoidosis, familial hypocalciuric hypercalcaemia or metastatic disease, and two had parathyroid carcinoma. Fifteen patients (16 per cent) developed permanent hypoparathyroidism requiring vitamin D and/or calcium therapy and nine had permanent recurrent laryngeal nerve paralysis. Undetected adenomas (41 cases) and inadequate resection in hyperplastic disease (28) were the predominant causes of initial failure. Reoperation for persistent or recurrent hyperparathyroidism restored normocalcaemia in the majority of patients. This 'cure' was achieved at the cost of considerable morbidity and a careful risk-benefit analysis of each patient is recommended before performing reoperative parathyroid surgery.