A pituitary adenoma was removed transsphenoidally from a 20-yr-old woman with secondary amenorrhea, galactorrhea, and hyperprolactinemia. Light and electronic microscopy, immunocytology characterized a prolactin cell tumor. The patient also underwent three surgical explorations for hyperparathyroidism. Only after selective catheterization of thyroid veins with radioimmunoassay for parathormone, an intrathyroidal parathyroid adenoma was found. No other case of proven prolactin adenoma in Wermer's syndrome has been reported.