Background: We examined how adolescents’ sleep patterns (i.e. insomnia symptoms and sleep duration) change from early- to mid-adolescence and whether adolescents follow different trajectories. Furthermore, we also examined the characteristics of adolescents within different trajectories, with a specifc focus on the role of school-related stress. We used three longitudinal waves of questionnaire data collected annually from a sample of Swedish adolescents (n = 1294; Mage = 13.2 [range: 12–15 years], SD = .42; 46.8% girls). Using established measures, the students reported on their sleep duration, insomnia symptoms, and perceived school-stress (including stress of school performance, peer and teacher relations, attendance, and school-leisure confict). We used latent class growth analysis (LCGA) to identify adolescents’ sleep trajectories, and the BCH method to describe the characteristics of the adolescents in each trajectory. We found four trajectories for adolescents’ insomnia symptoms; (1) low insomnia (69%), (2) low-increasing (17%, ‘emerging risk group’), (3) high-decreasing (9%), (4) high-increasing (5%; ‘risk-group’). For sleep duration, we found two trajectories; (1) ~8 h suffcient decreasing (85%), (2) ~7 h insuffcient- decreasing (15%; ‘risk-group’). Adolescents in risk-trajectories were more likely to be girls and consistently reported higher levels of school stress, particularly regarding school performance and attending school. School stress was prominent among adolescents suffering from persistent sleep problems, especially insomnia, and deserves further attention.