STUDIES OF CHROMOSOME ABNORMALITIES IN THE GENERAL POPULATION OF SEVERAL DIFFERENT COUNTRIES AND AMONG MALE PATIENTS OF MENTAL HOSPITALS, ADULT AND JUVENILE MALE OFFENDERS, AND MALE OFFENDERS COMMITTED TO MENTAL HOSPITALS ARE ENCOMPASSED IN THE OVERVIEW. THESE STUDIES SHOW THAT THREE TYPES OF SEX CHROMOSOME ABNORMALITIES--XXY, XYY, AND XXYY--ARE ASSOCIATED WITH CRIMINAL BEHAVIORAL DISORDERS. MEMBERS OF ALL THREE GROUPS MAY EXHIBIT MENTAL SUBNORMALITY, BUT THERE IS EVIDENCE THAT FOR SOME XXY AND XYY MALES MENTAL SUBNORMALITY IS LARGELY OR WHOLLY DISSOCIATED FROM BEHAVIORAL DISORDERS. THERE IS INSUFFICIENT EVIDENCE TO SUGGEST A RELATIONSHIP BETWEEN CHROMOSOME ABNORMALITIES AND PHYSICAL AND BEHAVIORAL ABNORMALITIES IN XXY MALES, BUT THERE IS GOOD EVIDENCE THAT THE ABNORMAL COMPLEMENT OF Y CHROMOSOMES STRONGLY INFLUENCES THE BEHAVIOR OF PHYSICALLY NORMAL XYY MALES. ALTHOUGH DATA ARE NOT AS YET CONCLUSIVE, THERE APPEAR TO BE DIFFERENCES BETWEEN THE BEHAVIORAL DISORDERS OF XXY AND XYY MALES. IT IS PROBABLE THAT THERE IS A GREATER COMPONENT OF AGGRESSIVE (PARTICULARLY SEXUALLY AGGRESSIVE) BEHAVIOR AMONG THOSE WITH AN EXTRA X CHROMOSOME THAN AMONG THOSE WITH AN EXTRA Y. SUPPORTING DATA AND A LIST OF REFERENCES ARE INCLUDED. (AUTHOR ABSTRACT MODIFIED--LKM)