The three major sources of delinquency are perceived to be the juvenile's personality and characteristics, the juvenile's family, and the immediate sociocultural environment (including delinquent peer group pressure). The authors examined 150 juvenile probation officers' reports in a Midwestern city and surrounding suburbs (102 from 1967-70 and 48 from 1961-63). The dependent variable was the probation officer's recommended disposition of the case. Independent variables were seriousness of offense, social factors relating to the juvenile's background, and the perceived cause of the juvenile's problem behavior. Data analysis revealed that the officers' own interpretation of who or what factors were responsible for the delinquency was the chief criterion used in reaching a decision. Previous studies of juvenile court decisionmaking were inconclusive because these studies did not take into account the process by which decisionmakers interpret delinquency and its causes. Tables and 27 reference notes are supplied.