RESEARCHERS FOUND CONSIDERABLE AMBIGUITY IN THE LITERATURE ABOUT THE PRECISE MEANING OF VARIOUS TERMS RELATING TO MENTAL RETARDATION, AND A PAUCITY OF RESEARCH MATERIAL ON THE DIFFICULTIES ENCOUNTERED BY THE RETARDED IN THE CRIMINAL JUSTICE SYSTEM. TOPICS ADDRESSED INCLUDE THE NATURE AND PREVALENCE OF MENTAL RETARDATION, LEGAL PROVISIONS FOR THE INTERROGATION OF SUSPECTS, INTERROGATION OF THE MENTALLY RETARDED, THE USE OF CONFESSIONS AND STATEMENTS IN EVIDENCE, AND THE AMERICAN PERSPECTIVE. ALTHOUGH THE MENTALLY RETARDED CONSTITUTE ONLY A TINY PROPORTION OF THE BRITISH AND AMERICAN POPULATIONS (2 AND 3 PERCENT, RESPECTIVELY), THERE HAS BEEN A HISTORIC TENDENCY TO ASSOCIATE MENTAL DEFICIENCY WITH SOCIAL DEVIANCE. STUDIES OF PRISON POPULATIONS HAVE SHOWN A HIGHER INCIDENCE OF MENTAL RETARDATION AMONG PRISONERS THAN IN THE POPULATION AS A WHOLE. ALTHOUGH BRITISH POLICE ARE FORBIDDEN TO USE COERCIVE METHODS OF QUESTIONING SUSPECTS, RETARDED INDIVIDUALS ARE LIKELY TO MISUNDERSTAND WHY THEY ARE BEING QUESTIONED, THE SIGNIFICANCE OF THE QUESTIONS, AND THE POSSIBLE CONSEQUENCES OF THEIR ANSWERS. ENCOURAGING SIGNS FOR THE TREATMENT OF THE MENTALLY RETARDED INCLUDE THE ISSUANCE OF A CIRCULAR BY THE BRITISH HOME SECRETARY TO THE POLICE DRAWING ATTENTION TO THE NEED FOR SPECIAL CARE IN THE INTERROGATION OF MENTALLY HANDICAPPED PERSONS. IT SUGGESTS THAT THE REQUIREMENT OF THE PRESENCE OF A THIRD PERSON, ALREADY REQUIRED IN THE CASE OF MENTALLY HANDICAPPED CHILDREN, SHOULD BE EXTENDED TO MENTALLY HANDICAPPED ADULTS. FOOTNOTES AND A BIBLIOGRAPHY ARE INCLUDED.