GREAT DIFFICULTY EXISTS IN COMPARING THE LEGAL AND MEDICAL CRITERIA OF MENTAL ILLNESS OR ABNORMALITY. ALTHOUGH SOME FORMS OF BEHAVIOR AND ACTIONS FORMERLY CONSIDERED CRIMINAL ARE NOW NONCRIMINAL (E.G., ATTEMPTED SUICIDE AND HOMOSEXUALITY BETWEEN CONSENTING ADULTS IN ENGLAND), THE TOTAL AMOUNT OF PUBLIC HOSTILITY TO DEVIANTS APPEARS STATIC, SO THAT LESS ANIMOSITY DIRECTED AT ONE TYPE OF CRIME ALLOWS MORE ATTENTION TO BE DIRECTED AT ANOTHER. ANOTHER SERIOUS PROBLEM IN TRYING TO COLLECT INFORMATION ON THE RELATIONSHIP BETWEEN MENTAL ILLNESS AND CRIME IS THAT OF FINDING THE OFFENDERS. ABOUT 70 TO 80 PERCENT OF OFFENDERS DO NOT GET ARRESTED, ALTHOUGH THOSE OFFENDERS WHO ARE MENTALLY ILL ARE MORE EASILY DETECTED AND ARRESTED. ONCE THEY COME BEFORE A COURT THEY ARE RAPIDLY DISTRIBUTED IN DIFFERENT DIRECTIONS--TO DIFFERENT FORMS OF LIBERTY OR DIFFERENT SORTS OF PRISON IF SENTENCED--SO THAT NO ONE GROUP IS EVER TRULY REPRESENTATIVE. OTHER PROBLEMS CONCERN MEDICAL DIAGNOSIS AND CATEGORIZATION FOR RESEARCH PURPOSES. REMARKABLE PROGRESS HAS BEEN MADE IN MAKING CLINICAL EXAMINATIONS MORE OBJECTIVE AND UNIFORM AND IN MEASURING THE VARIATION BETWEEN DOCTORS. TOOLS SUCH AS THE ENGLISH PRESENT STATE EXAMINATION AND THE CATEGO SYSTEM USED BY THE WORLD HEALTH ORGANIZATION, AS WELL AS THE VIDEO TAPE INTERVIEW, IN WHICH APPEARANCE, MODE OF EXPRESSION, AND SPEECH CAN BE TAKEN INTO CONSIDERATION IN MAKING DIAGNOSES, HAVE GREATLY AIDED CLINICAL EXAMINATIONS AND DIAGNOSIS. DISCUSSION OF THE LITERATURE REVEALS DIFFERENCES AMONG VARIOUS COUNTRIES IN DIAGNOSIS OF SCHIZOPHRENIA, MANIA, AND DEPRESSIVE PSYCHOSES, AS WELL AS EXTREME DIFFERENCES IN DIAGNOSIS OF SCHIZOPHENIA IN TWO COUNTRIES, THE U.S. AND THE U.S.S.R. SPECIFIC FINDINGS FROM ENGLISH STUDIES ARE CONSIDERED IN DETAIL, BOTH FOR GROSSLY ABNORMAL OFFENDERS AND FOR JUVENILE AND ADOLESCENT OFFENDERS WHO MOSTLY HAVE LESSER NEUROTIC OR PERSONALITY DISORDERS. THE LITERATURE SUGGESTS THAT THOSE SUFFERING FROM MENTAL DISORDERS HAVE NO GREATER TENDENCY TO COMMIT CRIME THAN OTHER MEMBERS OF SOCIETY, BUT SPECIAL CIRCUMSTANCES EXIST BETWEEN CERTAIN TYPES OF CRIME AND CERTAIN SPECIFIC DISORDERS WHICH WARRANT SPECIAL INVESTIGATION. TABLES AND REFERENCES ARE INCLUDED. (PRG)