The author presents data on the use of the insanity defense to provide a basis for current debates on its revision. Generally, the experience in New York State in 1976--1978 reflects an increasing number of insanity acquittals over 1965--1976, but the characteristics and length of hospitalization of the defendants remained fairly similar. In addition, in some counties the defense was used often, but in others it was not used at all. The author suggests that similar, more sophisticated analyses of the actual operation of the insanity defense be carried out to establish an adequate basis for designing rational social policy.