Recent research has shown that depression, anxiety disorders, and psychosis are more common than previously supposed in elderly populations without dementia. It is unclear whether the frequency of these disorders increases or decreases with age. Clinical expression of psychiatric disorders in old age may be different from that seen in younger age groups, with less and often milder symptoms. Concurrently, comorbidity between different psychiatric disorders is immense, as well as comorbidity with somatic disorders. Cognitive function is often decreased in people with depression, anxiety disorders, and psychosis, but whether these disorders are risk factors for dementia is unclear. Psychiatric disorders in the elderly are often related to cerebral neurodegeneration and cerebrovascular disease, although psychosocial risk factors are also important. Psychiatric disorders, common among the elderly, have consequences that include social deprivation, poor quality of life, cognitive decline, disability, increased risk for somatic disorders, suicide, and increased nonsuicidal mortality.