Adolescence associates with alterations in sleep-wake organization, such as later circadian phase preference. Simultaneously external pressures, such as evening-driven social activities increase. These may lead to delayed sleep phase, which may cause serious problems for waking up at socially accepted times, and absenteeism from the school may follow. This project aims at tracking risk factors for later circadian regulation problems, characterizing interconnections of biological, psychological and behavioural mechanisms that maintain or induce poor sleep regulation in adolescence, and building a cost-effective, theoretically-based sleep intervention for adolescents with delayed sleep phase. This randomized control trial capitalizes on a new population-based cohort of 16-17-year olds.

Inclusion Criteria:

• Late bedtime several times per week

Exclusion Criteria:

• Chronic disease that affects sleep. Ongoing therapeutic treatment relationship if considered overlapping by the participant