It is well recognized that a serious form of renal disease may result from hyperparathyroidism.1It is also well established that chronic renal insufficiency frequently is associated with secondary hyperplasia of the parathyroid glands.2On a priori grounds, therefore, one can reason that a paradoxic situation might exist wherein long-standing renal disease resulting from a parathyroid adenoma is so severe as to stimulate further overactivity of the other parathyroid glands. Actually this does occur. Johnson3reported a case in which removal of a parathyroid adenoma was followed by death from hypertension and uremia four years later, at which time the remaining parathyroid glands showed enlargement and hyperplasia. The following case report is submitted because it is the first to our knowledge in which secondary parathyroid hyperplasia has been proved to coexist with a parathyroid adenoma. REPORT OF CASE A. C., a former insurance salesman, aged 50, entered