A mental disorder, also called a mental illness, psychological disorder or psychiatric disorder, is mental or behavioral pattern that causes either suffering or a poor ability to function in ordinary life. Many disorders are described.Conditions that are excluded include social norms.omatoform disorders may be diagnosed when there are problems that appear to originate in the body that are thought to be manifestations of a mental disorder. This includes somatization disorder and conversion disorder. There are also disorders of how a person perceives their body, such as body dysmorphic disorder.