The identification of delinquent youth is not simply a matter of locating names and related data in police and court files. Two nonofficial methods are suggested to obtain data on juvenile delinquents and measure juvenile delinquency, self-reports and victim reports. The National Assessment of Juvenile Corrections found that slightly less than 2.5 percent of youth are referred annually to juvenile courts for delinquency. Petitions alleging property offenses constitute the largest single category for referral, followed by status offenses, violent crimes, and drug or alcohol offenses. Juvenile courts also receive cases of child dependency, abuse, and neglect. Various studies show that the relation between the frequency and seriousness of delinquent behavior and being officially defined as delinquent is positive, strong, and broadly generalizable. Studies involving age and gender reveal a great deal of variation in delinquent behavior, although more males than females become juvenile delinquents. Several studies report that a relatively few adolescents account for a high proportion of all serious criminal behavior committed by young people. Other studies also reveal considerable variation in delinquency according to race and social class. Differences in risk of offending, examined in terms of social variables, are not as pronounced among those who admit they are frequently and seriously involved in criminal behavior. These individuals, however, are distinguished by a high frequency of prior offending, early onset of delinquency, and drug use. 52 notes, 2 tables, and 1 figure