Personality disorders are a group of psychiatric conditions, each with specific chronic behavior patterns that are serious enough to cause problems with relationships, the ability to lead a constructive life and to maintain employment.

The behaviors can be traced back to at least adolescence or early adulthood and cannot be explained by another psychiatric condition, medical condition or drug use. Some personality disorders diminish during middle age without any treatment while others persist throughout life despite treatment.

Of the various personality disorders, antisocial personality disorder is considered to be one of the most violent and aggressive while obsessive-compulsive disorder is one of the most prevalent and recognizable. However, personality disorders such as histrionic personality disorder and narcissistic personality disorder are far less recognizable due to their symptoms being masked by explanations of extroversion and high self-esteem. Consequently, personality disorders such as these are harder to diagnose and treat.

Physicians use the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (abbreviated DSM-IV) as a tool during the diagnostic process. To qualify as a particular personality disorder the patient's behavior must meet a certain number of criteria laid out in the DSM-IV. Because many personality disorders have characteristics in common (antisocial and paranoid personality disorders, for instance) and symptoms of disorders can be caused by another underlying medical condition (such as anxiety disorder or substance abuse), it is important that all other causes of the patient's behavior be ruled out before a diagnosis is made.