Adenomas of the parathyroid gland, the majority of which contain mixed cell populations, are the most frequent cause of primary hyperparathyroidism. Parathyroid adenomas composed exclusively of water-clear cells are exceptionally rare. Until now, only 2 cases have been reported in English literature. We report a water-clear cell adenoma of the parathyroid gland in an intrathyroidal position, which has not been described previously according to our knowledge. HUM PATHOL 32:889-892. (C) 2001 by W.B. Saunders Company.