The principal objectives of this study are to describe trends over time in self-reported participation in crime or other problem behaviours and in victimization among youths in Sweden. Amongst other things, the article addresses the question of whether the small group that might be labelled high-frequency offenders has become more active over time. Another question examined is that of whether there are differences in the proportions reporting participation in crime and exposure to crime across youths from different backgrounds. These questions are examined on the basis of data collected in six nationally representative questionnaire surveys of youths in their final year of compulsory education (during the years 1995-2005), with sample sizes of between 5,300 and 8,200 respondents. Generally speaking, the proportion reporting that they have committed an offence of some kind has not increased since 1995. Instead the prevalence of several types of crime has decreased over time. No indication has been found that those youths who do commit offences have become more active over time. The reduction in the prevalence of involvement in crime remains when the focus is directed at differences between different socio-demographic groups. The proportions exposed to theft, threats, and serious violence have remained relatively constant over the period examined. The central impression produced by the findings about youth victimization is that of consistent and in some instances rather striking differences in the risk for victimization among youths from different social backgrounds.