The ability to measure serum prolactin levels has led to the characterization of hyperprolactinemia as a clinical entity. In women galactorrhea and amenorrhea are symptoms of elevated prolactin levels; in men, impotence seems to be a clinical correlate. In the differential diagnosis, concern about the presence of a pituitary adenoma is preeminent. Management of microadenomas is controversial; both active therapy and conservative follow-up have been advocated. For larger lesions, neurosurgery or radiation becomes necessary. Drug therapy to reduce prolactin levels is now available.