Over a four-year period 31 consecutive patients have undergone surgical exploration with a preoperative diagnosis of primary hyperparathyroidism. Persistent hypercalcemia remains the best diagnostic test. A high incidence of diabetes mellitus was found in this group of patients. Selective arteriography for localization of an adenoma prior to the initial surgery is discouraged. A successful operation could be predicted by the rapid fall in serum calcium level by the 16th hour. Twenty-eight of the 31 patients have remained normocalcemic.