ABSTRACT: The Past 15 years have witnessed several advances in knowledge about primary hyperparathyroidism. Incidence studies have revealed it to be a disease of aging. Known etiologies now include prior radiation exposure and several familial syndromes. Diagnosis has been simplified by a new generation of radio-immunoassays for parathyroid hormone. The natural history of mild hyperparathyroidism, as revealed by a single study, is one of a stable or slowly progressive disorder, with approximately half of those observed for 10 years showing sufficient progression or new complications to mandate surgery. The course of untreated hyperparathyroidism of more severe degree has not been well documented. Only two medical treatments have been shown to produce beneficial biochemical effects, namely neutral phosphate and estrogens; each is appropriate only for a narrow target group. Surgical treatment is safe and highly effective in experienced hands, and published data suggest a very low rate of recurrence after resection of parathyroid adenomas. Real time, high resolution ultrasonography is proving to be an effective tool for preoperative evaluation of the location and number of abnormal parathyroids.