BETWEEN 1959 AND 1961, THE INTRODUCTION OF IMPROVED TECHNIQUES OF CHROMOSOME ANALYSIS LED TO THE IDENTIFICATION OF A NUMBER OF HUMAN SEX CHROMOSOME ABNORMALITIES--47,XYY CHROMOSOMES IN MALES AND 45, X AND 47,XXX CHROMOSOMES IN WOMEN. THESE THREE TYPES OF ABNORMALITIES COULD BE IDENTIFIED USING NUCLEAR SEXING TECHNIQUES ON BUCCAL SMEARS. NUCLEAR SEXING SURVEYS LATER IDENTIFIED A NUMBER OF MALES WHO, ON CHROMOSOME ANALYSIS, HAD A 48,XXYY KARYOTYPE, WITH A POSSIBLE PROPENSITY TO ANTISOCIAL BEHAVIOR. ACTING ON THE POSSIBILITY THAT THIS BEHAVIOR MIGHT BE DUE TO THE EXTRA Y, AN EDINBURGH GROUP CONDUCTED A CHROMOSOME SURVEY AT MAXIMUM SECURITY HOSPITAL AT CARSTAIRS, SCOTLAND, WHICH LED TO THE IDENTIFICATION OF MALES WITH THE 47,XYY KARYOTYPE IN COMPARATIVELY LARGE NUMBERS. THE CONCLUSIONS THAT WERE DRAWN CONCERNING THE MENTAL DISORDERS OF THE 47,XYY MALES WERE THAT INTELLECTUAL CAPACITY, SEXUAL INSTINCT, AGGRESSIVE IMPULSES, AND EMOTIONAL RESPONSES WERE ALL CONSISTENT WITH IMMATURITY, DEFECTIVE DEVELOPMENT, OR INADEQUATE CONTROL, AND IN THE ABSENCE OF OTHER PREDISPOSING FACTORS, IT WAS REASONABLE TO DEDUCE THAT THE DISORDER COULD BE ATTRIBUTED TO THE EXTRA Y CHROMOSOME. FINDINGS OF STUDIES DONE IN THE UNITED STATES, ENGLAND, AND CANADA INDICATED THAT THE INCIDENCE OF 47,XYY MALES IN THE GENERAL POPULATION IS APPROXIMATELY 1 TO 1.5 IN EVERY 1,000. FRENCH STUDIES SHOW THAT 3 MEN OUT OF 1,875 HAVE THE CHROMOSOME ABNORMALITY. OUT OF A TOTAL OF 100 MEN IN ENGLISH PSYCHIATRIC HOSPITALS, RESEARCHERS IDENTIFIED 5 WITH EXTRA Y CHROMOSOME. ESTIMATES OF THE INCIDENCE OF 4,XYY MALES IN THE GENERAL POPULATION MADE ON THE FREQUENCY OF THIS ABNORMALITY IN NEWBORN MALE POPULATIONS INDICATE FAIRLY CLEARLY THAT THE EXTENSIVE STUDIES CARRIED OUT IN HOSPITALS FOR THE MENTALLY SUBNORMAL, MENTALLY ILL, AND PENAL INSTITUTIONS HAVE IDENTIFIED ONLY A SMALL MINORITY OF THESE MEN. STUDIES ALSO SUGGEST THAT PERSONS WITH A 47,XYY CHROMOSOME COMPLEMENT ARE AT AN INCREASED RISK OF DEVELOPING CHARACTER DISORDERS POSSIBLY CORRELATED WITH PSYCHOPATHY. TABULAR DATA AND REFERENCES ARE PROVIDED. (DAG)