THE POPULATION SAMPLED CONSISTED OF ALL MALE DANISH CITIZENS BORN TO WOMEN WHO WERE RESIDENTS OF COPENHAGEN, DENMARK, BETWEEN JANUARY 1, 1944 AND DECEMBER 31, 1947. INFORMATION ABOUT THE HEIGHT OF THESE MEN WAS OBTAINED FROM DRAFT BOARD RECORDS WHERE POSSIBLE. A CUTOFF POINT OF 184 CENTIMETERS WAS USED IN COMPOSING THE TALL GROUP SO THAT SEX CHROMOSOME ANOMALIES COULD BE SOUGHT. THE RESULTING GROUP CONSISTED OF 4,591 MEN, THE TOP 15.9 PERCENT OF THE HEIGHT DISTRIBUTION IN THE TOTAL GROUP OF 28,884. BLOOD SAMPLES AND BUCCAL SMEARS WERE SUCCESSFULLY USED IN DETERMINING CHROMOSOMAL CONSTITUTION FOR 4,139 OF THE MEN. FOR THIS SAMPLE, DATA FOR FIVE VARIABLES WERE OBTAINED: HEIGHT, CONVICTIONS FOR CRIMINAL OFFENSES, LEVEL OF INTELLECTUAL FUNCTIONING AS INDICATED BY SCORES ON AN ARMY SELECTION TEST AND BY EDUCATIONAL ATTAINMENT, AND PARENTAL SOCIAL CLASS AT THE TIME OF THE SUBJECT'S BIRTH. AMONG THE MEN FOR WHOM SEX CHROMOSOME DETERMINATIONS WERE MADE, 12 XYY'S AND 16 XXY'S WERE IDENTIFIED. THIRTEEN MEN WERE IDENTIFIED AS XY'S WITH OTHER CHROMOSOMAL ANOMALIES. THE REMAINDER, ALL IDENTIFIED AS HAVING THE NORMAL XY COMPLEMENT, CONSTITUTED THE CONTROL GROUP. WHILE THE INITIAL OBJECTIVE OF THE RESEARCH PROJECT WAS TO DETERMINE WHETHER XYY'S FROM THE TOTAL GENERAL POPULATION HAVE AN ELEVATED CRIME RATE, A CONCOMITANT OBJECTIVE WAS TO IDENTIFY INTERVENING VARIABLES THAT MIGHT MEDIATE THE RELATION BETWEEN AN EXTRA Y CHROMOSOME AND INCREASED ANTISOCIAL BEHAVIOR. THE THREE VARIABLES EXAMINED WERE AGGRESSIVENESS, INTELLIGENCE, AND HEIGHT. REGARDING THE RATE OF CRIMINALITY, XYY'S HAD A HIGHER MEAN RATE OF CRIMINAL CONVICTIONS THAN DID THE XY CONTROLS. WITH REGARD TO THE POSSIBLE CORRELATES OF THE ELEVATED XYY CRIME RATE, HEIGHT AND AGGRESSION WERE NOT CONFIRMED AS SIGNIFICANT FACTORS, WHILE THE INTELLIGENCE MEASUREMENTS SHOWED THE XYY'S TO BE APPRECIABLY LOWER IN INTELLIGENCE THAN THE XY'S. MOREOVER, IN THE XY SAMPLE, CRIMINALITY SHOWED A SUBSTANTIAL RELATION TO INTELLECTUAL FUNCTIONING. IT IS INDICATED THAT INTELLECTUAL FUNCTIONING IS AN IMPORTANT MEDIATING VARIABLE IN THE INCREASED CRIME RATE AMONG XYY'S AS COMPARED TO XY'S. TABLES OF DATA ARE INCLUDED. (RCB)