In this study the investigators will examine the effects of melatonin and light therapy on delayed sleep phase syndrome in adolescents 16 up to 20 years old. 60 subjects will be randomized into four different groups; melatonin + light therapy (N=15), melatonin + placebo light (N=15), placebo + light therapy (N=15) and placebo + placebo light. This is a double-blinded treatment and the participants will receive this treatment for 2 weeks. Then they will be re-randomized into two groups; full treatment with light therapy + melatonin (N=30) and no treatment (N=30) for 3 months unblinded. The investigators will test the subjects pre-treatment, post 2 week treatment and after 3 months.