Persons with borderline personality disorder (BPD) and related traits appear in many forensic psychiatry settings. Their clinical hallmarks affecting judgment, insight, impulsivity, motivations, and regulation of emotions, as well as their frequently chaotic lives (internal and external), inaccurate perceptions, rationalizations, and comorbid syndromes can have a marked effect on many civil, criminal, and institutional (eg, corrections) issues. Individuals with BPD are overrepresented in civil, criminal, and child custody forensic situations. The character psychopathology of these individuals is substantial, but is often not obvious to laypersons, including lawyers, judges, and jurors. The presence of BPD rarely affects basic responsibility for the person's actions, nor does it usually compromise most forms of competency. Function, not diagnosis, is the key arbiter of forensic relevance. BPD is associated with an increase in the likelihood of doctor-patient problems, including patient complaints and lawsuits that may not be deserved. Forensic professionals evaluating persons with BPD and related traits should be aware of personal and professional bias, particularly that associated with true countertransference.