EARLY STUDIES IN SCOTLAND HAVE GIVEN RISE TO STILL OTHERS AROUND THE WORLD ADDRESSING THE ROLE PLAYED BY THE XYY SYNDROME IN CONTRIBUTING TO MALE CRIMINALITY. ON THE BASIS OF EXISTING EVIDENCE, THE FREQUENCY OF 47,XYY MALES AT BIRTH APPEARS TO BE ABOUT 1.5 PER 1,000. A STRIKING FIGURE OF THE STUDY FINDINGS IS THE OBSERVATION THAT THE MEAN HEIGHT OF THE 47,XYY SUBJECTS IS CONSIDERABLY GREATER THAN THAT OF 46,XY (NORMAL) MALES. APART FROM HEIGHT, MANY OTHER PHYSICAL ABNORMALITIES HAVE BEEN FOUND, INCLUDING MONGOLISM, NEUROLOGICAL DEFECTS, SKELETAL DISORDERS AND DEFORMITIES, MARFAN'S SYNDROME, HYPOGONADISM, MYOPIA, AND VARICOSE VEINS. CERTAIN OTHER INTELLECTUAL AND BEHAVIORAL CHARACTERISTICS ARE ALSO MANIFEST. THE FINDINGS WITH RESPECT TO INTELLIGENCE ARE BIASED TOWARDS SUBNORMALITY, ALTHOUGH IT SHOULD BE NOTED THAT A BIAS TOWARD LOW INTELLIGENCE IN PENAL GROUPS--THE SUBJECTS OF MOST XYY STUDIES--MAY NOT BE ENTIRELY INDEPENDENT OF BEHAVIOR. THE VERY HIGH PREVALENCE OF 47,XYY MALES FOUND IN MAXIMUM SECURITY HOSPITALS SUGGESTS AN ASSOCIATION WITH DISTURBED BEHAVIOR OF SOME SIGNIFICANCE. SOME OF THE FINDINGS SHOW A PATTERN OF PETTY CRIMINALITY RATHER THAN OVERT AGGRESSION, WHILE OTHERS HAVE INDICATED A PROPENSITY TOWARD SUCH VIOLENT CRIMES AS MURDER AND RAPE. REFERENCES AND TABULAR DATA ARE PROVIDED. (KBL)