School-based physical education (PE) programs provide regular and structured opportunities for youths to participate in moderate or vigorous physical activities that help meet the Canadian public health recommendation for 90 minutes of daily physical activity. To examine prevalence and trends in PE participation among high school students (i.e., grades 9-12) in Ontario, Canada, during 1999-2005, researchers at the University of Toronto and the University of Guelph analyzed data from the Ontario Student Drug Use Survey (OSDUS). This report describes the results of that analysis, which indicated a significant linear decrease from 1999 to 2005 in the percentage of students who were enrolled in PE. Female and older students were least likely to be enrolled in PE and to participate in vigorous physical activity during the average PE class. As in the United States, coordinated programs involving schools, communities, and policy makers are needed to provide effective PE for all youths in Ontario.