Personality disorders are mental disorder with inflexible, enduring, maladaptive patterns of adjustment to life that cause either subjective distress or significant impairment of adaptive functioning.

The DSM-IV: Diagnostic and Statistical Manual of Mental Disorders (American Psychiatric Association) defines a personality disorder as an enduring pattern of inner experience and behavior that

• deviates markedly from the expectation of the individual's culture,
• is pervasive and inflexible,
• has an onset in adolescence or early adulthood,
• is stable over time, and
• leads to distress or impairment.