Functional change as a result of hospitalization is common, dynamic, and costly in both economic and human terms. It, however, is not an inevitable outcome of illness and aging. Older persons are substantial users of hospital care, and yet providers subject them to hospital practices that are more appropriate for younger patients. The information presented in this article suggests that our knowledge base regarding functional decline associated with hospitalization now allows us to identify high-risk patients and intervene both during and after hospitalization in order to maintain patient functioning.