Insomnia is prevalent (45%) in CHD patients and associated with significantly increased risk for recurrent cardiovascular events. Insomnia has recently been identified as the third most important risk factor for prognosis. However, very few insomnia patients are identified and receive treatment of insomnia today. CBT-I is the first-line treatment for insomnia, but studies on the effects in CHD patients are lacking. This project aims to document the effectiveness of Cognitive Behavioural therapy for insomnia (CBT-I) in an outpatient population with coronary heart disease (CHD). Furthermore, the biological and psychological mechanisms that may mediate the effects of the intervention will be identified. Finally, a health-economic simulation and a qualitative study of the participants experiences with CBT-I will be performed. This prospective, randomized, intervention study will continue until data have been collected for the primary outcome on 66 CHD outpatients with a diagnosis of insomnia assessed by Bergen Insomnia Scale (BIS). Participants will be randomised to a short, nurse-administered, CBT-I delivered in a group format or to sleep hygiene advice. The primary outcome will be remission from BIS-insomnia post-treatment and at 6-months follow-up. Secondary outcomes will be changes in insomnia severity, objective and subjective sleep parameters, daytime symptoms of insomnia, and quality of life. Exploratory outcomes include inflammation, cortisol, HbA1C, and cognitions/metacognitions. The project may document the effectiveness of CBT-I for a large patient-group with potentially favorable long-term effects on important clinical outcomes.