NEW YORK HAS ADOPTED AN INSANITY DEFENSE TO DEAL WITH SITUATIONS OF COGNITIVE AND DELUSIONAL IMPAIRMENT DUE TO MENTAL DISEASE OR DEFECT. A PERIOD OF POSTACQUITTAL TEMPORARY OBSERVATIONAL DETENTION ACCOMPANIES THE SPECIAL ACQUITTAL. TO DESCRIBE THE USE OF THE INSANITY DEFENSE IN THE STATE, TWO STUDY GROUPS ARE EXAMINED ACCORDING TO DEMOGRAPHIC CHARACTERISTICS, PRIOR HOSPITALIZATIONS, PRIOR ARRESTS, OFFENSES ON WHICH THEY WERE ACQUITTED, VICTIMS OF ACQUITTED OFFENSES, COURSE OF HOSPITALIZATIONS AFTER ACQUITTAL, AND CRIMINAL ACTIVITY AND HOSPITALIZATION AFTER RELEASE. THE FIRST GROUP CONSISTED OF 53 PERSONS ACQUITTED BEFORE 1965 AND THE SECOND WERE 225 PERSONS ACQUITTED FROM 1971-1976. RESULTS SHOWED THAT SUCCESSFUL USE OF THE DEFENSE HAS INCREASED MARKEDLY, THE DEFENSE IS NOT UNIFORMLY APPLIED THROUGHOUT THE STATE, IT HAS BEEN USED AS A GUILT-AVOIDANCE DEVICE FOR CERTAIN SEGMENTS OF SOCIETY, AND THE LEGAL STANDARDS FOR USE OF THE DEFENSE MAY NOT BE DECIDING FACTORS IN ITS SUCCESSFUL USE. QUESTIONNAIRES WERE SENT TO LEGAL PROFESSIONALS ACROSS THE STATE FOR THEIR VIEWS ON THE INSANITY DEFENSE. THE 239 RESPONSES SHOW THAT LEGAL PROFESSIONALS HAVE PROBLEMS WITH THE DEFENSE IN TERMS OF POOR STATUTORY DEFINITIONS, MOST FELT THAT THE DEFENSE SHOULD BE MODIFIED BY REMOVING THE AMBIGUITY AND VAGUENESS OF PSYCHIATRIC TESTIMONY, AND PERCEIVE THAT TREATMENT OF ACQUITTEES INSIDE A CORRECTIONAL SETTING IS PREFERABLE TO PSYCHIATRIC HOSPITALIZATION. THE EFFECTS OF THE DEFENSE ON SOCIETY, INDIVIDUALS, AND THE PSYCHIATRIC PROFESSION ARE DISCUSSED, AND PROBLEMS IN ADMINISTERING THE DEFENSE ARE CONSIDERED. THE PROGRAM PLAN AND ELEMENTS OF MENTAL TREATMENT INSIDE THE CORRECTIONAL SETTING IS EXAMINED, AND IT IS CONCLUDED THAT NEW YORK HAS DEVELOPED AN INTEGRATED PROGRAM ENSURING TREATMENT WHICH CORRECTS THE DEFICIENCIES OF PREVIOUS PROGRAMS. A SECTION ADDRESSES THE NEED FOR CHANGING THE INSANITY DEFENSE AND DISCUSSES OPTIONAL APPROACHES SUCH AS THE AFFIRMATIVE DEFENSE, A BIFURCATED TRIAL, AND A GUILTY BUT INSANE VERDICT. THE FINAL CHAPTER SETS OUT A PROPOSED RULE OF DIMINISHED CAPACITY. (DAG)