Psychogeriatrics began as an extension of psychiatry, with an emphasis on the unique manifestation of psychiatric disorders in the elderly. Early in the history of psychogeriatrics there was an emphasis on late-onset or late-enduring depression; paraphrenia and late-onset psychotic disorders; the late-life phases of schizophrenia; and anxiety and substance abuse disorders in the elderly. Growing recognition of the increasing frequency of Alzheimer's disease (AD) in the course of aging and the high prevalence of behavioral disturbances in patients with AD led psychogeriatricians to study the diagnosis and management of this disorder.