Personality disorders constitute a separate diagnostic category (Axis II) in the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders ( DSM). Unlike the major mental disorders (Axis I), which are characterized by periods of illness and remission, personality disorders are generally ongoing. Often, they first appear in childhood or adolescence and persist throughout a person's lifetime. Aside from their persistence, the other major characteristic of personality disorders is inflexibility. Persons affected by these disorders have rigid personality traits and coping styles, are unable to adapt to changing situations, and experience impaired social and/or occupational functioning. A further difference between personality disorders and the major clinical syndromes listed in Axis I of DSM-IV-TR ( DSM , fourth edition, text revised) is that people with personality disorders may not perceive that there is anything wrong with their behavior and are not motivated to change it. Although the DSM-IV-TR lists specific descriptions of 10 personality disorders, these conditions are often difficult to diagnose. Some characteristics of the various disorders overlap. In other cases, the complexity of human behavior makes it difficult to pinpoint a clear dividing line between pathology and normality in the assessment of personality. In still other cases, persons may have more than one personality disorder, complicating the diagnosis . There also has been relatively little research done on some of the personality disorders listed in DSM-IV-TR.