A review of 51 successful reoperations for persisting hypercalcaemia due to primary hyperparathyroidism shows that inadequate anatomical knowledge, inadequate surgical technique and unusual localizations of the parathyroids are the most frequent causes of failure of the primary operation. The majority of these failures are therefore preventable. There is a frequent need for cervical thymectomy in parathyroid surgery. Sternotomy is only very rarely necessary.