The aim of the study was to examine school-related determinants of self-reported health among adolescents. Questionnaire survey data comprising 4,972 students, Grades 7 through 9, from 20 schools in northern Sweden were used. Also, complimentary data about each school were collected from the Swedish National Agency for Education. Using multilevel logistic regression analyses, results showed that most variation in self-reported health was explained by individual-level differences. Truancy, bullying, and poor relations with teachers significantly increased the odds ratio of reporting poor general health, for boys and for girls. Most variables at the school level, for example, school size and student–teacher ratio, did not render significant associations with students’ self-reported health. In conclusion, this study indicates that health promotion at school, including school health services, may benefit from focusing primarily on individual-level determinants of health, that is, students’ relations to peers and teachers, without ignoring that bullying and weak student–teacher relationships also may induce school-level interventions.