The researchers examined records on Danish males born in Copenhagen from 1944 to 1947 who committed offenses recorded in the penal registers of local police offices. They then compared the data to that contained in a 1972 study of delinquent males born about the same time in Philadelphia. Although class, schooling, and IQ related to delinquency in similar ways in both cities, all three related more strongly to delinquency in Copenhagen. In both cities, violent offenders tended to have a lower social class standing, to have completed less schooling, to have lower IQ, and to begin committing offenses earlier. In Philadelphia, race and class were strongly correlated; this was not a factor in highly homogenous Danish society. Concentration of offenses per chronic offender was greater in Copenhagen, although that city had fewer chronic offenders. The two cohorts were not comparable in the area of offense specialization. The Danish sample demonstrated a moderate level of specialization among thieves and violent offenders. A major difference was in the peak age of delinquency: in Philadelphia, delinquency peaked during the time that most youngsters are still in school (age 16), but in Copenhagen, delinquency peaked after compulsory education ended at 17. In the United States, delinquency seemed to stem from frustration and alienation while Danish delinquents appeared to be reveling in the newfound freedom away from school. Similarities and differences are interpreted in detail according to frustration barrier theories and cultural theories. Notes, tables, and references accompany each chapter. The appendix discusses the offense seriousness scale used in the study.