Sleep disorders commonly co-occur with psychiatric disorders. Sleep disorders are often treated with medication or not at all in psychiatric care, although there exist a plethora of documentation of the effectiveness of sleep interventions. There is also an increase in studies showing effectiveness of sleep-interventions when the sleep disorder co-occurs with psychiatric illness. The most common and best documented treatment for insomnia is cognitive behavioral therapy for insomnia (CBTi). There is a great gap in the knowledge on how sleep disorders can be treated effectively in psychiatric care. In this project the investigators therefore seek to investigate the effect of non-pharmacological, group-based treatment in a randomized controlled trial (RCT) where sleep and psychiatric symptoms are the primary outcome measures. CBTi comprise of sleep education, sleep restriction, stimulus control and cognitive restructuring of dysfunctional thoughts about sleep.