SINCE EARLY STUDIES IN SCOTLAND AND SWEDEN SUGGESTING AN UNUSALLY HIGH PREVALENCE OF SEX-CHROMATIN POSITIVE MALES AMONG INMATES OF INSTITUTIONS FOR MENTALLY ILL OR RETARDED CRIMINALS, THE ASSOCIATION OF ABNORMAL COMPLEMENTS OF SEX CHROMOSOMES WITH ANTISOCIAL BEHAVIOR HAS BECOME WELL ESTABLISHED. STUDIES IN ENGLAND, EUROPE, AUSTRALIA, AND THE U.S. UNCOVERED VARIOUS ABNORMAL CHROMOSOME STRUCTURES AMONG ANTISOCIAL OFFENDERS, INCLUDING XYY, XYYY, XXY, AND XXXY. HOWEVER, THE XYY COMPLEMENT HAS RECEIVED THE MOST ATTENTION. IN ALL SOME 63 MALES WITH RECORDS OF CRIME OR ANTISOCIAL BEHAVIOR AND WITH XYY CHROMOSOME COMPLEMENTS HAVE BEEN REPORTED IN MEDICAL LITERATURE. SUCH FINDINGS RAISE SEVERAL PERTINENT QUESTIONS. DOES THE PRESENCE OF SUCH A GENETIC DEFECT LESSEN THE ETHICAL AND LEGAL RESPONSIBILITY OF AN INDIVIDUAL? IF IT DOES NOT MITIGATE GUILT, SHOULD IT MODIFY A SENTENCE? IS AN UNUSUALLY TALL BOY GROWING UP IN A A POOR ENVIRONMENT FORCED INTO AGGRESSIVE BEHAVIOR BY THAT ENVIRONMENT OR BY HIS EXTRA CHROMOSOME? AT WHAT POINT DOES AN ANTISOCIAL PERSON WITH ABNORMAL CHROMOSOMES CEASE TO BE A CRIMINAL UNDER THE JURISDICTION OF THE LAW AND BECOME A PATIENT UNDER THE CARE OF THE MEDICAL PROFESSION? REFERENCES ARE PROVIDED. (KBL)