ALMOST ALL REPORTS OF XYY INDIVIDUALS WITH ANTISOCIAL BEHAVIOR HAVE NOTED UNUSUAL HEIGHT. MANY REPORTS ALSO INDICATE THAT THE UNUSUAL HEIGHT IS PRESENT FROM CHILDHOOD ON. FOUR REASONS HAVE BEEN SUGGESTED FOR THE MISBEHAVIOR OF TALL OR LARGE CHILDREN: (1) LARGER CHILDREN MAY BE MORE SUCCESSFUL IN FIGHTS, (2) LARGER CHILDREN, APPEARING OLDER, MAY ELICIT GREATER SOCIAL AND INTELLECTUAL EXPECTATIONS FROM THEIR ELDERS THAN THEIR ABILITY WOULD WARRANT, (3) LARGER CHILDREN MAY BE SINGLED OUT OF A GROUP MORE OFTEN FOR CENSURE, AND (4) LARGER CHILDREN MAY TEND TO ASSOCIATE WITH OLDER CHILDREN WITHOUT ADEQUATE EXPERIENCE TO KEEP OUT OF TROUBLE. IF LARGE SIZE OR HEIGHT CONTRIBUTES TO MISBEHAVIOR IN XYY INDIVIDUALS DURING CHILDHOOD, THEN WE MIGHT EXPECT IT TO BE A SIGNIFICANT CHARACTERISTIC OF XY BOYS WHO HAVE COMMITTED ANTISOCIAL ACTS. ACCORDINGLY A STUDY OF THE INMATES OF TWO INSTITUTIONS FOR NONPSYCHOTIC OFFENDERS UNDER THE AGE OF 16 WAS CONDUCTED. THE POPULATION OF ONE INSTITUTION WAS MORE UNMANAGEABLE THAN THAT OF THE OTHER. IT WAS EXPECTED THAT THE HEIGHT OF THESE INMATES WOULD BE LOWER THAN AVERAGE BECAUSE OF POVERTY, NEGLECT, AND MALNUTRITION, BUT IT WAS SPECULATED THAT THESE INMATES MIGHT BE TALLER THAN AVERAGE BECAUSE OF THE HYPOTHESIS THAT LARGER OR TALLER CHILDREN TEND TO MISBEHAVE OR GET INVOLVED IN ANTISOCIAL ACTIVITY. THE HEIGHTS OF ALL THE INMATES WERE TAKEN AND THEIR HEIGHTS WERE CONSIDERED ACCORDING TO AGE-ADJUSTED STANDARDS BECAUSE OF THE VARIATIONS IN AGE. INMATES IN BOTH INSTITUTIONS WERE GROUPED BY RACE. THE WHITE CHILDREN IN THE INSTITUTION OF MORE MANAGEABLE CHILDREN WERE SIGNIFICANTLY SMALLER. HOWEVER, THE TOTAL POPULATION OF XY CHILDREN IN BOTH INSTITUTIONS WERE CLOSE TO STANDARD IN HEIGHT. THERE WERE THREE XYY CHILDREN (ONE WHITE, 2 BLACKS) IN THE INSTITUTION WITH THE MORE MANAGEABLE CHILDREN. THEIR INTELLIGENCE QUOTIENT RANGED FROM 1 TO 15 POINTS LOWER THAN THE AVERAGE OF BOYS OF THE SAME RACE AND AGE IN THEIR INSTITUTIONS. ALL THREE HAD HEIGHTS GREATER THAN THOSE AT THE 90TH PERCENTILE OF THE XY BOYS OF THE SAME RACE. THE DATA YIELDED BY THIS TEST INDICATE THAT LARGE HEIGHT PER SE DURING LATE CHILDHOOD IS NOT EXCLUSIVELY RESPONSIBLE FOR THE FREQUENCY OF DELINQUENCY AMONG XYY INDIVIDUALS. LIMITED REFERENCES ARE PROVIDED. (FCW)