Introduction: This paper examines secular trends in violence among Ontario students between 1983 and 2001, and variation by sex. Methods: Using data from the Ontario Student Drug Use Survey, we examined self-reports of assault, weapon carrying, and gang fighting based on 10 cross-sectional surveys from 1983 to 2001. Respondents were derived from representative samples of Ontario students in grades 7, 9, 11, and 13 (OAC) who completed in-class anonymous self-administered surveys. Data were weighted to account for the complex survey design and analyzed using logit trend analyses. Results: Short-term trends (1991-2001) showed assault, weapon carrying, and gang fighting have been on downward trajectories since the mid-1990s, reaching the lowest prevalence in 2001 among males and females. Long-term trends (1983-2001) among 11th-graders showed assault increased between 1985 and 1999, but declined in 2001. Gang fighting among males increased during the late 1980s and again during the mid-1990s, but declined between 1997 and 2001. Gang fighting among females remained at a stable, low level. Discussion: Future monitoring is necessary to understand whether the decline in self-reported violent behaviour among adolescents is robust.