Shared psychotic disorder and criminal responsibility: a review and case report of folie à trois.

We present a case of shared psychotic disorder involving three sisters who were successful in establishing an insanity defense on numerous felony charges in the South Carolina criminal court system. Two of the authors of this article were court-appointed examiners in this case. We then present a history of shared psychotic disorder, an overview of the use of this diagnosis in the defense of insanity, and a discussion of the disposition of individuals with "temporary insanity." Finally, we compare shared psychotic disorder, culturally based belief systems, and religious cults, with a focus on their common and contrasting characteristics.