Patients with primary hyperparathyroidism are usually seen because of chronic symptoms referable to the urinary tract, skeleton, or gastrointestinal tract. However, it has become evident that a few patients may first be seen with acute and rapidly progressive symptoms attributable only to a markedly elevated serum calcium. These symptoms include muscular weakness, anorexia, nausea, vomiting, constipation, thirst, polyuria, and nonspecific abdominal pain as well as disturbances in behavior and state of consciousness. This clinical state has been termed hyperhyperparathyroidism (1), parathyrotoxicosis (2), or acute hyperparathyroidism (3), and although the course of this syndrome is extremely variable, it may rapidly be