This condition manifests itself as an unwarranted tendency to interpret the actions of other people as deliberately threatening or demeaning. People with a paranoid personality disorder are suspicious of other people, and they are usually unable to acknowledge their own negative feelings towards others. The causes and means of preventing this disorder are unknown, but the incidence appears increased in families with a schizophrenic member. Histories of paranoid behavior are common, and a psychological evaluation is needed to confirm the diagnosis.

Treatment is difficult because the person's traits make it difficult to form a professional relationship. The health care provider should respect interpersonal distance, and avoid defensiveness or attempts at humor. Prognosis is poor; people with this disorder tend to resist treatment.