The research used data from all 575 persons who were born between 1957 and 1968 and suspected by the police of an industrial community in southern Sweden of having committed a crime between 1975 and 1977. The study also gathered information from people born earlier than 1957 but committing a crime with one or more people in the main study population and from persons who committed crime with someone in the main sample during the 1978-80 followup period. Thus, the total sample included 834 persons. Data came from police records, other agencies' records; and interviews with criminal justice, recreation and social service personnel and juvenile gang members. Results indicated that most juvenile delinquency consists of pleasurable acts committed in a group and that most groups in which crimes are committed are temporary. In addition, group members are recruited from a local social youth culture in which criminality represents an important form of relations. Furthermore, the degree of criminality of youth in a particular geographical area is unevenly distributed, and crimes are determined by opportunities, youths' ages, and their involvement in the criminal juvenile environment. Thus, influencing a youth's peer relationships can influence the youth's criminality. Tables, figure, appended instrument, tables, and diagrams depicting peer relationships and offenses