Many studies in England and the United States have established valid differences between the sexes regarding involvement with delinquency. The lower incidence of female criminality has been attributed to traditional expectations of female behavior, greater social control exercised over girls' activities, lack of opportunity, and conservative attitudes toward law and order held by females. This project explored sex differences in crime using questionnaires completed by subjects between the ages of 13 and 15 as part of a comprehensive urban crime survey in 1975. This sample attended a school in a working class area of Sheffield and were asked to answer items measuring attitudes toward the police, the extent of personal victimization, and criminal or deviant acts committed during the past 12 months. The responses were analyzed according to sex, age, and social class. Over half the sample were pro-police, while less than 10 percent expressed hostile opinions. However, girls were more willing than boys to see the police as interested in helping them and were overall more favorably disposed toward the police. Over two-thirds of the respondents reported having been the victim of at least one crime, usually involving thefts from the person or of possessions left unattended. Only 18 percent had ever reported the crime to the police. Boys were considerably more likely to be victims of crimes than girls. Offense types ranged from theft to avoiding paying the fare on public transport. Although girls were more likely to truant, on 16 of the 19 items on the crime checklist, boys were significantly more likely to offend. Age was positively related to truancy and involvement in corporate thefts for both boys and girls, but social class was not a significant factor. The self-report study also revealed a high degree of hidden delinquency, although there was no evidence to indicate that girls' delinquency was likely to remain more hidden. For both sexes, individuals with more hostile attitudes toward the police committed more delinquent acts. Implications of these findings for current theories on sex differences are discussed. Tables and 48 endnotes are included.