The "aging" of the world population is by now a well-recognized phenomenon. It has become a matter of concern to the social planner and deliverer of services, as weil as to the clinician. On aper capita basis, the aged-that is those 65 and older-appear in outpatient health care facilities at a rate wh ich is approximately fifty percent greater than their adult peers, stay about three times as long in general medical and surgical facilities, and represent more than 90 percent of the long-term-care beds in the United States. In addition, at a time when they represented approximately 10 percent of the total population, the aged were the recipients of 25 percent of all prescriptions for medication. Thus, an understanding of the drug use consequences, misuse and abuse of drugs among older persons, has become a salient issue for the scientist, clinical physician, and other health care professionals. The aged are a group at heightened risk for a number of disorders and often present with clinical problems not usually encountered in an aging population. Many such problems are the direct consequence of multiple, concurrent, and complicating disorders; drug/drug interactions, com­ pliance with physician prescription, the use of concurrent non-prescribed substances such as alcohol or over-the-counter medication, and a variety of other behaviors. There is also a growing interest in the well recognized, but poorly understood, pattern of organic changes which occur in later maturity.