A personality disorder is a type of mental disorder in which you have a rigid and unhealthy pattern of thinking, functioning and behaving. A person with a personality disorder has trouble perceiving and relating to situations and people. This causes significant problems and limitations in relationships, social activities, work and school. In some cases, you may not realize that you have a personality disorder because your way of thinking and behaving seems natural to you. And you may blame others for the challenges you face. Personality disorders usually begin in the teenage years or early adulthood. There are many types of personality disorder. Some types may become less obvious throughout middle age. Types of personality disorders are grouped into three clusters, based on similar characteristics and symptoms. Many people with one personality disorder also have signs and symptoms of at least one additional personality disorder. It's not necessary to exhibit all the signs and symptoms listed for a disorder to be diagnosed. Cluster A personality disorders are characterized by odd, eccentric thinking or behavior. They include paranoid personality disorder, schizoid personality disorder and schizotypal personality disorder.