TO EXAMINE OBSCURED AND VISIBLE ACTS OF JUVENILE DELINQUENCY, THE STUDY SURVEYED 1,084 ADOLESCENTS (AGES 12-18) FROM THE CITY OF MONTREAL, WITH A QUESTIONNAIRE LISTING 39 OFFENSES (INCLUDING VANDALISM, LARCENY, DRUG ABUSE) AND WERE ASKED TO INDICATE WHICH OF THE LISTED OFFENSES (IF ANY) THEY HAD COMMITTED. THE RESULTS REVEALED A CONSIDERABLE AMOUNT OF HIDDEN DELINQUENCY: 92.8 PERCENT OF THE YOUTHS ADMITTED TO HAVING COMMITTED AT LEAST 1 OFFENSE WITHIN THE PAST YEAR. THE MAJORITY OF CRIMES WAS COMMITTED BY MALE OFFENDERS OF VARIED SOCIAL BACKGROUND BETWEEN THE AGES OF 16 AND 17. MANY OF THESE OFFENSES WERE INSIGNIFICANT AGE-RELATED ACTS; SERIOUS OR REPEAT OFFENDERS WERE FEW. TO SURVEY THE DEVELOPMENT OF HIDDEN DELINQUENCY, THE SAME SAMPLE POPULATION WAS QUESTIONED AGAIN 2 YEARS LATER. THE RESULTS INDICATED THAT DELINQUENCY TENDS TO DECREASE WITH JUVENILES' PROGRESSIVE MATURITY AND COMING TO TERMS WITH SOCIAL NORMS. AS POLICE PROSECUTION TENDS TO INCREASE JUVENILE CRIMINAL ACTIVITIES BECAUSE OF THE STIGMATIZATION INVOLVED, POLICE SHOULD CHOOSE THE CASES IN WHICH THEY INTERVENE WITH GREAT CARE (I.E. ONLY SERIOUS OFFENSES). THE STUDY INCLUDES A GRAPH AND NUMEROUS STATISTICAL CHARTS. A BIBLIOGRAPHY AND THE QUESTIONNAIRE SUBMITTED TO THE JUVENILES ARE APPENDED. --IN FRENCH. (SAJ)