Throughout adult life, there is progressive alteration in body composition and tissue function. There is loss of lean body mass, notably by muscle, with a gain in body fat. We do not know whether nutritional factors affect these gross changes. In the case of loss of bone density (osteoporosis), however, there is evidence that the process is retarded by raising the intake of calcium and by exercise. Aging also adversely affects tissue function at the level of the whole organ and tissue as well as at the cellular and subcellular level. Animal models show similar age-related changes, and demonstrate further that alterations in nutrient intake or exercise can alter the rate of loss of tissue and cellular function. In addition to the effects of adult aging on tissue function, certain chronic diseases and disabilities are related to aging. These conditions include atherosclerosis, hypertension, coronary thrombosis, cancer, etc. Both human epidemiological studies and animal experiments on aging suggest strongly that nutrition plays a role in the onset and development of these conditions. There is a need for more accurate assessments of the nutrient needs of people over 65 years of age. A few selected nutrients are discussed. Studies of energy intake during adult life show a progressive reduction with increasing age, due mainly to reduced physical activity. Vitamin C levels in the white blood cells of elderly women can be half those of young adults; these respond to supplementary vitamin C without evidence of clinical benefit. Nitrogen balance studies suggest that the allowance of protein for older adults is not less than for young. Finally, surveys of elderly in whole populations and in selected groups show that, by the nutritional standards of young adults, there may exist a significant amount of malnutrition in people as they grow old, though we do not know whether this affects rate of loss of tissue function with age.