Data published in the past decade have demonstrated that adults who are deficient in growth hormone (GH) experience deleterious clinical consequences without treatment. In 1996, the Food and Drug Administration approved the use of GH in adults who were GH deficient as a result of hypothalamic or pituitary disease. However, there are other conditions in adults for which GH treatment has also been approved (acquired immune deficiency syndrome [AIDS]-related wasting) or for which it is being considered, such as aging, catabolic states, and cardiomyopathy. Clinical issues revolve around the rationale for treatment; the diagnostic evaluation; the effects of GH therapy on body composition, bone density, lipids, and cardiac function; and appropriate dosing and follow up. Clearly, the use of GH in adults raises reimbursement issues as well. In this article, Dr. Beverly M.K. Biller provides an overview of the rationale for the treatment of adult-onset GH deficiency and reviews its etiology and clinical features as well as reimbursement and utilization issues related to treatment. Dr. Mary Lee Vance discusses various assays and criteria used in the diagnostic evaluation of the patient with adult-onset GH deficiency. Dr. David L. Kleinberg focuses on the effects of GH therapy on body composition, bone density, lipid profiles, and cardiac function, as well as on reimbursement issues regarding body composition studies. To complete the clinical portion of this session, Dr. David M. Cook addresses dosing and follow up. To address economic implications, Dr. Terry Gordon provides the payer's perspective on the diagnosis and treatment of adult-onset GH deficiency.