LONG Y CHROMOSOMES WERE DEFINED AS THOSE EQUAL IN LENGTH TO OR LONGER THAN EACH OF THE F CHROMOSOMES. MARGINALLY LONG Y CHROMOSOMES WERE DEFINED AS THOSE WHERE IT WAS DIFFICULT TO DECIDE WHETHER THE Y CHROMOSOME WAS CONSISTENTLY LONG OR AVERAGE. MEDICAL, SOCIOLOGICAL, AND OTHER HISTORIES WERE OBTAINED FROM OVER 200 BORSTAL LADS; MORE LIMITED DATA WAS AVAILABLE FOR A SIMILAR NUMBER OF CONTROLS. IT WAS DISCOVERED THAT 37 OF THE CONTROLS HAD COMMITTED OFFENSES BEFORE OR DURING THE SURVEY AND A CHI SQUARE TEST SUGGESTED THAT CARRIERS OF THE LONG Y VARIANT HAD A HIGHER INCIDENCE OF DELINQUENCY. A COMPARISON OF PERSONALITY TRAITS ETC. WITHIN THE BORSTAL SAMPLE SHOWED THAT LADS WITH A MARGINALLY LONG Y VARIANT DIFFERED IN MANY ASPECTS FROM THE REST OF THE SAMPLE. THE IMPLICATIONS OF THESE FINDINGS ARE DISCUSSED IN RELATION TO QUESTION OF HEREDITARY CONTRIBUTIONS TO DELINQUENT BEHAVIOR. REFERENCES ARE INCLUDED.