In 1886, the French neurologist Pierre Marie proposed that the pituitary gland plays a fundamental role in the development of acromegaly. Since then, remarkable progress has been made in understanding hypophysial structure and function, the bio-chemistry of pituitary hormones, the regulation of pituitary hormone synthesis and release, and the morphologic and clinical manifestations of pituitary abnormalities. This chapter focuses on pituitary morphology in health and disease. Because the hypothalamus is closely related to the pituitary, diseases of the hypothalamus also are summarized.