Additional medical manpower will be required to meet the growth in the elderly segment of the United States population over the next 50 years. This paper provides estimates of the needs for medical geriatric manpower under four different models: continuation of the status quo; academic geriatricians only; provision of care by academic and consultant geriatricians; and provision of care by academic, consultant, and primary-care geriatric practitioners. Each option is further analyzed in terms of three levels of delegation to nonphysician clinicians. We project the implications of these 12 patterns through the year 2030, assuming present usage levels and allowing for improved care of the elderly. The need for geropsychiatric care is explored separately. We think that geriatricians should provide improved care, including both consultant and primary care, to people aged 75 years and older, and that they should delegate a moderate amount of responsibility to nurse practitioners, physician assistants, and social workers. On the basis of these assumptions, and allowing for an academic role as well, we estimate that the United States will require between 7000 and 10,300 geriatricians by the year 1990; the best intermediate figure is about 8000. (N Engl J Med. 1980; 302:1327–32.) DECLINING birth rates, together with modest increases in longevity, have ushered in an era of greater concern for the elderly. Although the term “elderly” is customarily applied to people more than 65 years old, the group over the age of 75 years is growing and is critically important to health-care providers. Persons more than 65 years old will constitute more than 12 per cent of the United States population by the end of this century, and almost half of that 12 per cent will be over 75 years of age. As a group, the elderly are characterized by declining health.