In endocrine pathology, surgical pathologists often concentrate on neoplasms at the expense of nonneoplastic disease processes. This is unfortunate as nonneoplastic endocrine disorders are many times more common in the population. As in all fields of medicine, nonneo plastic endocrine diseases can closely mimic the neoplastic; an awareness of all aspects of pathology underpins routine clinical practice. This Fifth Series Fascicle offers pathologists and clinicians an opportunity to develop an increased understanding of nontumor endocrine pathology in order to inform patient care.