OF THE 151, 5 WERE FOUND TO HAVE CHROMOSOME ABNORMALITIES--2 WITH KLINEFELTER'S SYNDROME AND 3 WITH THE XYY SYNDROME. THE INCIDENCE OF KLINEFELTER'S SYNDROME, 47,XXY WAS 1.3 PERCENT COMPARED WITH AN EXPECTED INCIDENCE OF 0.21 PERCENT. THE INCIDENCE OF THE XYY SYNDROME WAS 2.0 PERCENT COMPARED WITH AN EXPECTED FREQUENCY OF 0.15 PERCENT. ALL FIVE PATIENTS WERE TYPICALLY IMMATURE AND THOSE WITH KLINEFELTER'S SYNDROME HAD PRONOUNCED CONTACT DIFFICULTIES AND HARDLY ANY FRIENDS, A CONDITION CHARACTERISTIC OF PATIENTS WITH THE XYY SYNDROME. NONE OF THE FIVE WERE OPENLY AGGRESSIVE, ALTHOUGH THE PATIENTS WITH THE XYY SYNDROME WOULD OCCASIONALLY APPEAR AGGRESSIVE DUE TO IMPULSIVITY AND LACK OF BRAKING MECHANISMS. ALL FIVE HAD BEEN INVOLVED IN PROPERTY CRIMES, ALTHOUGH ONE OF THE 47,XXY HAD BEEN CHARGED WITH SEXUAL CRIMINALITY WITH A 13 YEAR OLD GIRL. THAT THE INCREASE IN THE SIZE OF THE Y CHROMOSOMES IS DUE TO AN ACTUAL INCREASE IN THE Y CHROMOSOME SUBSTANCE IS INDICATED BY THE FINDING OF A COMPARATIVELY HIGH FREQUENCY OF MALES WITH A LARGE Y CHROMOSOME IN THE CRIMINAL SAMPLE AND A HIGH FREQUENCY OF CRIMINALITY AND MENTAL ILLNESS AMONG FATHERS AND BROTHERS, BUT NOT AMONG BROTHERS AND SISTERS. THIS INDICATES THAT THERE IS A CONNECTION BETWEEN THE SIZE OF THE Y CHROMOSOME AND THE RISK OF PERSONALITY DEVIATION AND CRIMINALITY AND THAT THE SIZE OF THE Y CHROMOSOME IS INHERITABLE. TABULAR DATA AND REFERENCES ARE INCLUDED. (KBL)