Patients follow the fully standard sleep test according to the normal procedure. This means that they undergo a polysomnography and fill in a questionnaire. If according to the questionnaire, there is insomnia, the patient also receives an intake interview to check whether this is indeed the case. If the patient has both disorders and meets the inclusion and exclusion criteria, they will be asked to sign the informed consent. If the patient agrees, the CPAP-therapy will be started as usual, simultaneously with CGT-i. The latter will last 7 weeks and will cover the following points: psycho-education, sleep restriction and sleep hygiene, cognition, relaxation and relapse prevention. Because of the design of this study (starting CGT-I as soon as possible after the diagnosis of OSAS) and the groups already planned for CBT-I, it is not possible for all participants to participate in group cognitive behavioral therapy, therefore individual sessions were provided for these participants. The patient comes for monitoring at set times.

Inclusion Criteria:

• All patients, male and female, with an OSAS diagnosed by full polysomnography and insomnia diagnosed by questionnaires.
• Age between 18 and 75 years
• Dutch as native language

Exclusion Criteria:

• Patients younger than 18 years and older than 75 years
• Patients with a burn-out
• Patients with restless legs
• Pregnant woman
• Patients who work as shift workers
• Patients with severe psychiatric disorder
• Patients who take sleep medication, unless it can be reduced and stopped during cognitive behavior therapy
• Patients with daily alcohol abuse (men > 3 drinks on any day or 14 per week, women > 2 drinks on any day or 7 per week)