At the heart of the problem of establishing criminal responsibility for persons with MPD is the fact that Anglo-American theories of responsibility developed largely before MPD and other forms of severe dissociation were understood and traditional rules of criminal responsibility do not address the unique phenomenology of MPD. The article reviews how courts understand and assess criminal responsibility; gives an overview of how courts have applied the doctrine of criminal responsibility to individuals with MPD; explains what legal theorists say about this question; and uses a case example to illustrate how various theorists would assess the responsibility of a criminal defendant with MPD. The lack of consensus over how to handle cases with MPD has left judges, juries, and experts in a quandary. The central disagreement concerns which aspect of the defendant's psyche is to be assessed; the answer to that question is what distinguishes the differing conclusions in legal cases. The challenge is the complexity of the issue, which implicates law, psychiatry, ethics, and philosophy. Notes, references