The object of this study is to determine whether feedback added to a self-help protocol for insomnia enhances the treatment effect. In this study all participants receive an online self-help cognitive behavioral therapy (CBT) intervention consisting of information (psycho-education) about sleep and cognitive-behavioural exercises. Adult persons with insomnia will be invited via a popular scientific website to fill out online questionnaires. Half of the participants will received by e-mail from a therapist, the other half of the participants will do the intervention without feedback. Participants will be measured 4, 16, and 40 weeks after intervention with the same questionnaires.