THE 825 MONTREAL, QUEBEC, ADOLESCENTS WERE A RANDOM SAMPLE FROM PUBLIC AND PRIVATE SCHOOLS AND FROM DETENTION CENTERS, TAKEN IN 1974, WHEN THEY WERE AGES 12 TO 16. THE SAME SAMPLE WAS REVIEWED IN 1976. EACH ADOLESCENT WAS ADMINISTERED A QUESTIONNAIRE REGARDING FAMILY, SCHOOL, ACTIVITIES, FRIENDS, AND DELINQUENCY. THE QUESTIONNAIRE WAS USED TO DISCOVER HOW THESE ADOLESCENTS' PSYCHOSOCIAL DEVELOPMENT COMPARED WITH THEIR DELINQUENCY. STUDY RESULTS SUGGESTED THAT DURING ADOLESCENCE CRIMINAL DELINQUENCY PROGRESSES UNTIL THE ADOLESCENT REACHES 15 YEARS OF AGE, WHEN DELINQUENCY BEGINS TO DIMINISH FOR THE MAJORITY AND TO CONTINUE FOR THE MINORITY. THESE DEVELOPMENTS APPEAR TO PARALLEL DEVELOPMENTS IN THE SOCIAL, PSYCHOSOCIAL, AND PSYCHOLOGICAL LIVES OF ADOLESCENTS. THE TRANSITION FROM STUDENT TO NONSTUDENT AND THE ADOPTION OF A WORKER ROLE SEEM TO BE POWERFUL MECHANISMS IN REGULATING DELINQUENCY, WITH DELINQUENCY DECREASING CONSIDERABLY AS RESPONSIBILITY IS ASSUMED. THE PSYCHOSOCIAL TIES (ATTACHMENTS, BELIEFS) THAT ADOLESCENTS FORM APPEAR TO HAVE A SOCIAL, ROLE-CREATING FUNCTION THAT ALSO HELPS TO REGULATE DELINQUENCY. FINALLY, PERSONALITY TRAITS, REFLECTING THE FORMATION OF A POSITIVE PERSONAL IDENTITY, EMERGE AS REGULATING MECHANISMS, REINFORCING THE EFFECTS OF STATUS AND PSYCHOSOCIAL TIES, AND BRINGING ABOUT DECREASES IN DELINQUENCY. THE PSYCHOSOCIAL DEVELOPMENT THAT OCCURS DURING ADOLESCENCE IS THUS A PROCESS OF DISCOVERING THE BOUNDARIES OF BEHAVIOR WITHIN SOCIETY AND FINDING, THROUGH MATURATION, WAYS TO CONFORM TO OR DEAL WITH SOCIETAL NORMS. GIVEN THESE FINDINGS, PREVENTIVE MEASURES SHOULD FOCUS ON ADOLESCENTS' PSYCHOSOCIAL DEVELOPMENT THROUGH A POLICY OF MINIMAL INTERVENTION, WHERE ADOLESCENTS CAN EXPLORE THE BOUNDARIES OF BEHAVIOR, BUT GUIDANCE IS GIVEN TO SHOW WHERE THOSE BOUNDARIES ARE. REFERENCES AND TABLES ARE APPENDED. --IN FRENCH.