Personality disorders are enduring patterns of inner experience and behavior that deviate markedly from those expected by the individual's culture; these inflexible and pervasive patterns reflect issues with cognition, affectivity, interpersonal functioning and impulse control, and lead to clinically significant distress or impairment in social, occupational, or other important areas of functioning. The AMA Guides to the Evaluation of Permanent Impairment, Fourth Edition, defines two specific personality disorders, in addition to an eleventh condition, Personality Disorder Not Otherwise Specified. Cluster A personality disorders include paranoid, schizoid, and schizotypal personalities; of these, Paranoid Personality Disorder probably is most common in the legal arena. Cluster B personality disorders include antisocial, borderline, histrionic, and narcissistic personality. Such people may suffer from frantic efforts to avoid perceived abandonment, patterns of unstable and intense interpersonal relationships, an identity disturbance, and impulsivity. Legal issues that involve individuals with cluster B personality disorders often involve determination of causation of the person's problems, assessment of claims of harassment, and assessment of the person's fitness for employment. Cluster C personality disorders include avoidant, dependent, and obsessive-compulsive personality. Two case histories illustrate some of the complexities of assessing impairment in workers with personality disorders, including drug abuse, hospitalizations, and inpatient and outpatient psychotherapy.