Dissociative Identity Disorder (DID) (formerly known as Multiple Personality Disorder) is a condition in which a person appears to possess more than one personality, and sometimes very many. Some recent criminal cases involving defendants with DID have resulted in "not guilty" verdicts, though the defense is not always successful in this regard. Walter Sinnott-Armstrong and Stephen Behnke have argued that we should excuse DID sufferers from responsibility, only if at the time of the act the person was insane (typically delusional); otherwise the presumption should be that persons with DID are indeed responsible for their actions. We find their interpretation of DID and of the way in which the requirements for criminal insanity relate to this condition worrying and likely to result in injustice to DID sufferers. Our thesis is that persons with DID cannot be responsible for their actions if the usual features of the condition are present. A person with DID is a single person in the grip of a very serious mental disorder. By focusing on the features of DID which have, as we argue, the effect of deluding the patient, we try to show that such a person is unable to fulfill the ordinary conditions of responsible agency (namely, autonomy and self-control).