The authors review the recent literature on multiple personality disorder (MPD), the most severe and chronic of the dissociative disorders, in relation to court cases of competence to stand trial, the insanity defense, and research on malingerers feigning MPD. Issues relevant in the assessment of competency and insanity are described. Features characteristic of MPD, including amnesia and alterations in consciousness and personality, have varying degrees of influence over the criminal behavior of an individual with MPD. As in other psychiatric disorders, the influence of MPD on an individual's competence to stand trial, and sanity, can be evaluated systematically. This article discusses a specific diagnostic tool, the Structured Clinical Interview for DSM-IV Dissociative Disorders (SCID-D), an extensively field tested instrument that is potentially quite useful in forensic assessment of suspects manifesting dissociative symptoms and disorders. The particular advantages of the SCID-D will be reviewed in the context of some well known criminal cases involving MPD. Further research using diagnostic interviews for the systematic assessment of dissociative symptoms and MPD in criminal cases will continue to clarify the influence of these symptoms in a forensic context.