THE STUDY SUBJECTS INCLUDED 59 INSTITUTIONALIZED JUVENILES AGED 13 TO 19, 80 MALE INMATES AGED 18 TO 25, AND 31 MENTALLY ILL PATIENTS WITH CRIMINAL RECORDS. UNLIKE STUDIES THAT HAVE SOUGHT CHROMOSOME ABNORMALITIES ONLY AMONG TALL OFFENDERS (BECAUSE OF THE LINK BETWEEN ABNORMALITIES AND TALLNESS), THERE WAS NO SELECTION FOR HEIGHT. TWO INMATES HAD THE XYY CHROMOSOME ABNORMALITY, ONE THE XXY ABNORMALITY. NO ABNORMALITIES WERE DETECTED AMONG THE MENTALLY ILL OFFENDERS. NONE OF THE CHROMOSOMALLY ABNORMAL INMATES SHOWED ANY CLINICAL ABNORMALITY. ALL WERE OF AVERAGE INTELLIGENCE. THE FINDINGS OF THIS SCREENING AND OF OTHER CHROMOSOME STUDIES SUGGEST THAT, WHILE AN EXTRA Y CHROMOSOME IS A PREDISPOSING FACTOR IN CRIMINAL BEHAVIOR, IT PROBABLY CARRIES NO MORE WEIGHT IN THIS RESPECT THAN OTHER, AS YET UNDETERMINED GENETIC OR ENVIRONMENTAL FACTORS. THE BACKGROUNDS AND CHARACTERISTICS OF THE CHROMOSOMALLY ABNORMAL INMATES ARE DESCRIBED BRIEFLY. A LIST OF REFERENCES IS INCLUDED, ALONG WITH A SUMMARY IN GERMAN. (LKM)