Hyperparathyroidism due to adenoma of the parathyroids has been recognized as a distinct disease entity, which is amenable to surgical therapy, for 25 years. An important addition to knowledge about the disease, resulting from the work of Fuller Albright and his colleagues, has been the recognition that in some instances hyperparathyroidism may be caused by generalized hyperplasia of all the parathyroid glands, rather than by adenoma alone. This generalized hyperplasia differs sharply from secondary hyperplasia of the parathyroids due to chronic renal disease in that it is a "primary disease," just as adenoma is. The hyperfunction caused by adenoma is indistinguishable by clinical or laboratory examination from primary hyperplasia. Primary hyperplasia of the parathyroids occurs in only about 9% of the cases of hyperparathyroidism,1and only 27 cases have been reported in the literature. The coexistence of a duodenal ulcer in this case is also of interest, as will