AbstractReoperation for persistent or recurrent hyperparathyroidism is more hazardous than is primary cervical exploration and is also much less likely to result in cure of the disease. Only 21 of 34 reoperations (62%) were successful during the period 1970 through 1972 at the Mayo Clinic, compared with success in 312 of 327 primary operations (95%). In 9 patients who had their initial exploration at this institution, the most common cause of failure at the first operation was inadequate treatment of multiglandular disease; in 25 patients who were first operated on elsewhere, missed adenomas were far more common.Parathyroid arteriography and selective venous sampling with parathyroid hormone assays should improve the results of reoperation by providing preoperative localization of hyperfunctioning parathyroid glands in difficult cases. These procedures, however, are expensive and technically difficult, and they are not always successful. They are also associated with a definite morbidity, which must be weighed against any anticipated benefits. The systematic evaluation and treatment of patients facing reoperation for hyperparathyroidism should be undertaken in special centers accustomed to dealing with these difficult problems.