The 'demographic imperative' of a progressively aging society will place unprecedented demands on the health care system in the 21st century. Although improved education, public health measures, personal lifestyles, and health care will result in a large proportion of those born surviving to old age in robust health and vitality, the sheer numbers of 'baby-boomers' who will become the elderly and the inevitable association between aging and the associated multiple, especially chronic diseases and physiological impairments of old age will require more efficient and more effective systems of health care to meet the needs of the aging population. Generalists, specialists, and medical and surgical subspecialists will play important roles in meeting these needs, often in the multidisciplinary mode. Geriatricians will directly provide but a small minority of the care, focusing upon education, research, and consultation and in delivering primary care to the frail elderly and especially in long term care. Collaboration with subspecialists will be frequent in all these domains. Nephrologists, who already practice multidisciplinary team care of frail, complicated, chronically ill patients with end-stage renal disease, have much to contribute as their patient population progressively grows in numbers and age. Hence geriatricians and nephrologists have much to learn from and contribute to each other in addressing the 'age wave' of the 21st century.