Mental disorder that is marked by deeply ingrained and lasting patterns of inflexible, maladaptive, or antisocial behaviour to the degree that an individual's social or occupational functioning is impaired.
Rather than being illnesses, personality disorders are enduring and pervasive features of the personality that deviate markedly from the cultural norm. They include the dependent, histrionic, narcissistic, obsessive-compulsive, antisocial, avoidant, borderline (unstable), paranoid, and schizoid types. The causes appear to be both hereditary and environmental. The most effective treatment combines behavioral and psychotherapeutic therapies (see behaviour therapy ; psychotherapy ).