This report describes mental health, physical health, and risk behaviours among students in 2015 and changes since 1991, where available. Although OSDUHS began in 1977, most physical health and mental health indicators were introduced in the survey in the early 1990s. In this report, trend results are provided for two analytical groups of students: those in grades 7 through 12, and those in grades 7, 9, and 11 only. The first group is used to assess 2015 estimates and relatively recent trends (1999-2015), and the second is used to assess long-term trends (1991-2015). All data are based on self reports derived from anonymous questionnaires administered in classrooms between November 2014 and June 2015. New indicators in this report include subjective social status at school, usual numbers of hours of sleep on a school night, going to bed hungry, elevated stress, and symptoms of attention-deficit/hyperactivity disorder (ADHD).