Depression in late life is a treatable disorder and is not a part of the normal aging process, points out Ira R. Katz, M.D., a professor of psychiatry at the University of Pennsylvania Medical Center. Primary-care doctors, however, often overlook or misdiagnose depression in older people (those over age 75), said Dr. Katz. Of those older persons who are depressed, only one in six will be properly diagnosed and treated. More than 80% of these people could be treated effectively with antidepressants or other forms of therapy. Methods to prevent depression include staying active socially and maintaining a high level of physical fitness.