Galactorrhea, or inappropriate lactation, is a relatively common problem that occurs in approximately 20 to 25 percent of women. Lactation requires the presence of estrogen, progesterone and, most importantly, prolactin. Stress, suckling, sleep, sexual intercourse and medications may increase prolactin levels, whereas dopamine inhibits its release. The differential diagnosis of galactorrhea includes pituitary adenomas, neurologic disorders, hypothyroidism, numerous medications, breast stimulation, chest wall irritation and physiologic causes. The evaluation includes a thorough history and physical examination, as well as selected laboratory and imaging studies to rule out secondary causes such as an intracranial mass or a tumor. Diagnostic studies include a pregnancy test, a prolactin level, renal and thyroid function tests and, if indicated, magnetic resonance imaging of the brain. Treatment options for prolactinomas include observation, dopamine agonists, surgery and radiation therapy, depending on tumor size and associated symptoms. Fortunately, the prognosis for patients with prolactinomas is good: most prolactinomas remain stable or regress. In pregnant women, prolactinomas must be observed closely because the lesions may greatly increase in size.