BECAUSE PREVIOUS STUDIES HAD SHOWN AN ASSOCIATION BETWEEN STATURE AND THE XYY CHROMOSOME ABNORMALITY, CHROMOSOME ANALYSES WERE PERFORMED ON 37 OF THE 42 INMATES AT THE HERSTEDVESTER FACILITY WHO WERE 180 CENTIMETERS (APPROXIMATELY 5 FEET, 11 INCHES) TALL OR TALLER. ANALYSES SHOWED 2 PATIENTS TO HAVE THE ABNORMAL CHROMOSOME CONSTITUTION 47,XYY--1.29 PERCENT OF ALL 155 PATIENTS AT THE INSTITUTION AND 5.4 PERCENT OF THE PATIENTS EXAMINED. THE EXPECTED FREQUENCY FOR THIS ABNORMALITY IN THE GENERAL ADULT MALE POPULATION IS BETWEEN 0.10 AND 0.18 PERCENT. THE 2 PATIENTS WERE AMONG 12 WITH A STATURE OF AT LEAST 184 CENTIMETERS (SLIGHTLY OVER 6 FEET) AND AMONG 5 WHO HAD COMMITTED ARSON. (ONLY 3 OF THE 35 PATIENTS WITH NORMAL CHROMOSOME CONFIGURATIONS HAD COMMITTED ARSON). THE MAIN TYPE OF CRIMINALITY FOR BOTH CHROMOSOMALLY ABNORMAL PATIENTS WAS AGAINST PROPERTY (PETTY THEFT, BURGLARY OF SUMMER HOMES), ALTHOUGH ONE HAD BEEN SENTENCED FOR SEXUAL INDECENCY AND VIOLENCE. BOTH HAD PERSONALITIES CHARACTERIZED AS AGGRESSIVE WITH PERIODS OF VIOLENT, DESTRUCTIVE BEHAVIOR. THE RESULTS OF THIS STUDY AND OF OTHERS SUGGEST THAT CRIMINAL PSYCHOPATHS WITH A HEIGHT OF 180 CENTIMETERS OR MORE SHOULD BE GIVEN A CHROMOSOME CHECK, ESPECIALLY IF THEY HAVE COMMITTED ARSON. DETAILED CASE HISTORIES OF THE CHROMOSOMALLY ABNORMAL INMATES, SUPPORTING DATA, AND A LIST OF REFERENCES ARE INCLUDED. (LKM)