RESEARCH IN THE FIELD OF HUMAN GENETICS HAS DETECTED SEVERAL CHROMOSOME ABNORMALITIES, AND SOME OF THESE HAVE BEEN DETERMINED TO PRODUCE DEVELOPMENTAL DISORDERS. MANY PATIENTS WITH AN EXTRA X CHROMOSOME HAVE BEEN FOUND IN HOSPITALS FOR THE MENTALLY SUBNORMAL, AND HAVE HAD RECORDS OF CRIMINAL BEHAVIOR. IT IS NOT CLEAR, HOWEVER, WHETHER THE EXTRA X CHROMOSOME DIRECTLY PREDISPOSES DISTURBED BEHAVIOR, OR WHETHER THE DELINQUENCY CAN BE EXPLAINED BY THE REDUCED INTELLECT. A CHROMOSOME SURVEY OF MALE PATIENTS AT THE SCOTTISH STATE HOSPITAL FOR DANGEROUS PATIENTS FOUND THAT NEARLY 3 PERCENT OF THE POPULATION HAD AN EXTRA Y CHROMOSOME. MEN WITH THE XYY COMPLEMENT HAD NO PHYSICAL ABNORMALITY NOR ANY CONSPICIOUS ABNORMAL SEXUAL DEVELOPMENT. SOME WERE MENTALLY RETARDED, BUT OTHERS WERE OF NORMAL INTELLIGENCE. ALL OF THOSE WITH THE XYY TRAIT HAD A HISTORY OF OFFENSIVE BEHAVIOR AND MOST HAD CRIMINAL RECORDS. IT IS STRONGLY SUGGESTED THAT THE EXTRA Y CHROMOSOME IS RESPONSIBLE FOR THE CRIMINALITY AND MORAL DEFICIENCY OF THESE PATIENTS. FURTHER RESEARCH SHOULD DETERMINE THE INCIDENCE OF THE XYY ABNORMALITY IN THE GENERAL POPULATION.