Comprehensive geriatric assessment has been well defined as a multidimensional—usually interdisciplinary—diagnostic process designed to quantify an elderly individual's medical, psychosocial, and functional capabilities and problems with the intention of arriving at a comprehensive plan for therapy and long-term follow-up.

This approach to decision making and developing plans for the care of older patients with complex problems at critical points in their lives has developed from the experience and observations of clinicians involved in the care of older persons over the last three quarters of the century.

Many older people acquire chronic diseases that in turn result in varying degrees of disability. This is clearly not true for all elderly people; some in their 80s and 90s continue to be vigorous in all aspects of life. However, the number of older people who have some degree of impairment in carrying out their usual functions does increase in the later years, with over 70% of those aged 80 and older reporting some limitation in activity. Such older people may be referred to as frail elderly and they are the ones who are likely to need some form of long-term assistance of care to continue to maintain as much independence in living as possible.

To determine the types of assistance needed by geriatric patients, the physician and other health care professionals must conduct a comprehensive diagnostic evaluation or assessment that is fully analogous to the careful diagnosis that must precede any type of treatment decision. The medical conditions that underlie and contribute to the functional losses must be identified and appropriately treated, but this is only a part of the necessary effort. The types and degrees of functional losses themselves must be carefully addressed within the context of the family and other social supports available to help meet the older person's needs and achieve his or her individual goals.