MENTAL RETARDATION IS DEFINED AS SUBAVERAGE INTELLIGENCE EXISTING CONCURRENTLY WITH SIGNIFICANT DEFICITS IN ADAPTIVE BEHAVIOR AND ORIGINATING DURING THE FIRST 18 YEARS OF LIFE. THE CONCEPT OF MENTAL RETARDATION IS DISCUSSED IN DETAIL, INCLUDING A DESCRIPTION OF THE CONDITION, ITS PREVALENCE, IDENTIFICATION AND CLASSIFICATION, AND ITS RELATIONSHIP TO CRIMINAL ACTIVITY. THOUGHT ON CRIMINAL RESPONSIBILITY IN ANGLO-SAXON LAW OVER THE YEARS IS TRACED IN ORDER TO PROVIDE A HISTORICAL PERSPECTIVE. CONTEMPORARY RULES REGARDING CRIMINAL RESPONSIBILITY ARE THEN EXAMINED, BEGINNING IN 1843 WITH THE M'NAGHTEN RULES. THESE ESSENTIALLY CONSIST OF A TEST OF THE DEFENDANT'S KNOWLEDGE OF LAW AND MORALS. OTHER TESTS CONSIDERED ARE THE IRRESISTIBLE-IMPULSE RULE, THE PRODUCT RULE, AND THE MODEL PENAL CODE STANDARD AND VERMONT RULE; THE PROVISIONS OF EACH AND THEIR MAJOR CRITICISMS ARE OUTLINED. IN ADDITION, THE ISSUE OF ABOLITION OF THE INSANITY DEFENSE IS EXAMINED. THE PUNISHMENT VERSUS TREATMENT CONTROVERSY IS DISCUSSED. THE CONCEPTS THEMSELVES ARE EXPLORED TO DISTINGUISH THE THEORETICAL DIFFERENCES BETWEEN THEM. THEN THE ACTUAL PERFORMANCE OF PRISONS (DESIGNED FOR PUNISHMENT) AND MENTAL HEALTH INSTITUTIONS (DESIGNED FOR TREATMENT) ARE PRESENTED, ALONG WITH A DISCUSSION OF THE DEVELOPMENT AND HISTORY OF THESE FACILITIES. THE CONCEPT OF NORMALIZATION (I.E., THE BELIEF THAT THE MENTALLY RETARDED SHOULD BE ALLOWED TO LEAD AS NORMAL A LIFE AS POSSIBLE) AND ITS SIGNIFICANCE FOR DETERMINING CRIMINAL RESPONSIBILITY ARE EXAMINED. RECOMMENDATIONS ARE MADE FOR CHANGING METHODS OF DETERMINING CRIMINAL RESPONSIBILITY AMONG MENTALLY RETARDED OFFENDERS, AND A DISCUSSION IS PRESENTED OF WHAT CONSIDERATIONS THE COURT SHOULD TAKE INTO ACCOUNT WHEN DECIDING THE DISPOSITION OF A CASE IN WHICH THE DEFENDANT HAS BEEN FOUND NOT RESPONSIBLE. THE PRIMARY RECOMMENDATION CONCERNS THE IMPLEMENTATION OF A PROCEDURE WHICH WOULD ALLOW THE DECISION OF CRIMINAL RESPONSIBILITY FOR A PARTICULAR PERSON TO BE MADE OUTSIDE OF THE EMOTIONAL ATMOSPHERE OF A CRIMINAL PROCEEDING. REFERENCES ARE PROVIDED.