On the basis of observational studies, (1)(2)(3)(4)(5)(6)(7)(8) hypopituitarism has an increasing prevalence with increasing age. • On the basis of case reports and observational studies, (3)(4) septo-optic dysplasia is the most common congenital cause of hypopituitarism. On the basis of epidemiologic studies, (1)(2)(3)(4)(5)(6)(7)(8)(9) (10)(11) other causes of hypopituitarism include genetic or anatomic abnormalities (including midline facial defects), trauma, mass effect, infection, and autoimmune and infiltrative diseases. On the basis of case reports and expert opinion, single detected pituitary hormone deficiencies are rarely isolated and should prompt evaluation of the other pituitary hormones. Pituitary hormone values may be inappropriately normal in the setting of end-organ hormone deficiency. On the basis of expert opinion and case reports, (9) clinical features of hypopituitarism can initially be subtle and vary based on the hormones involved, although poor linear growth is a prominent finding in many deficiencies and should prompt consideration of further testing. On the basis of expert opinion, diabetes insipidus is characterized by loss of free water from an inability to concentrate the urine that results in hypernatremic dehydration if untreated.