Geriatrics, specialized branch of medicine that deals with the diseases of older persons and their therapy. The study of the aging process itself is called gerontology. Rising interest in geriatrics is due largely to the greater number of older persons in society, which is in turn a result of social and medical changes that have extended the life expectancy in the United States from an average of 47 years in 1900 to 76.3 years in 2000. The elderly population is expected to increase significantly, with the number of persons over 85 growing most rapidly.

In 1975 the U.S. Congress established the National Institute on Aging (NIA) to sponsor research on aging and on therapy for the problems of older persons. In 1978 the Institute of Medicine of the National Academy of Sciences issued a report recommending greater integration of knowledge on aging and geriatrics into the curriculum of medical schools. Some physicians have advocated establishing special geriatric care units in hospitals and outpatient health clinics. Nevertheless, Robert Butler, the first director of the NIA, identified one of the limits to advancing the study of geriatric medicine when he observed that traditional medical education trains physicians to think in terms of cure. This concept is not usually applicable in geriatrics, as many medical conditions of elderly persons can only be ameliorated, not cured.

While some elderly people experience mental impairment, studies indicate that illness—not age—may be responsible. Treatable causes of mental deterioration include alterations in functioning of the thyroid gland, sleep disorders, depression resulting from bereavement, infectious and metabolic diseases, and the side effects of therapeutic drugs. This last cause is especially important, because the average person over age 65 takes 13 different medicines in a year. Because some of these drugs may interact and cause toxic effects, and because human metabolism clears drugs from the body less rapidly as people get older, an increased probability exists of interference with mental function. Physicians treating older persons must be alert to these effects.

Mental changes in the elderly may also be due to irreversible conditions, such as Alzheimer's disease. No cure exists for this degenerative disease; the course of the illness is variable, usually leading to death within five to ten years. Mental impairment can also result from stroke.

Older persons are also more susceptible to diseases generally found in people of all ages, due in part to the weakening of the immune system as witnessed by their increased risk of death from influenza infection or exposure to cold. Heat, too, is more dangerous to the elderly. During serious heat waves the mortality rate among persons over the age of 65 can be more than ten times greater than that among other age groups.

In addition, progressive diseases tend to become more severe in old age. These include heart disease, arthritis, diabetes mellitus, glaucoma, cataracts, and cancer.