Multiple personality disorder (MPD) is a growing phenomenon in the United States. The number of cases have mounted following the celebrated cases of 'Three Faces of Eve' and 'Sybil' that have been popularized over the past several decades. How can--or should--the criminal law deal with multiple personality? Should the defendant suffering MPD be deemed competent to stand trial, or be able successfully to assert the insanity defence, or diminished capacity or automatism? Does MPD qualify as a mental disease or defect under the test of criminal responsibility, which would call for commitment upon a finding of not guilty by reason of insanity? What is the effect of MPD on cognition or control? These issues are discussed.