Pituitary tumors are common, but cause significant disease related to the production of excess hormone(s), interference with the normal function of the pituitary gland, and compression of adjacent structures. The pituitary gland is about the size of a dime and is centrally located in the head, behind the eyes. The most common pituitary tumors are prolactinomas, that present with amenorrhea, infertility and galactorrhea in women and with impotence and loss of libido in men. Patients with growth hormone secreting tumors may have joint pain, carpal tunnel syndrome, muscle weakness, sleep apnea, hypertension, congestive heart failure, diabetes mellitus and colon cancer. Adrenocorticotropin-secreting pituitary tumors present with centripetal obesity, muscle weakness, easy bruisability, hirsutism, amenorrhea, diabetes mellitus, hypertension and osteoporosis. Other pituitary tumors arise in thyrotrope cells, resulting in excessive thyroid gland function, and in gonadotrope cells, that often do not secrete any functional hormone. Headaches, visual disturbances and abnormal pituitary function may result from local growth of the tumor.