Objective: ADHD is characterized by the progressive development of, impulsiveness, attentional difficulties and sometimes also excessive hyperactivity. Main biological reason is a quantitative reduction of the neurotransmitter dopamine in the forebrain. A lack of dopamine is also typical for depressive disorders. Methods: Bright light therapy is proven to be effective in treating depression. Purpose of our study is to verify the therapeutic effectiveness of Bright light therapy in subjects affected by ADHD. Results: Results show a significant improvement which lasts for at least 4 weeks, which is superposed by regulation of the circadian rhythm. Initial decrease of especially morning saliva melatonin levels, due to regular sleep under in-patient conditions, is followed by symptom improvement and a raising evening melatonin level, due to activation during the day. This level decreases as soon as activation is ceased. Conclusion: Bright light therapy seems to be effective as add-on therapy for ADHD, but in fact, stabilization of the circadian rhythm is the most important therapeutic intervention, either for ADHD or for depression, as demonstrated in another study.