Obstructive sleep apnea (OSA) is a condition where the patient's breathing cease during sleep due to collapse of the oro-pharynx. The consequences are reduced quality of sleep, increased risk for developing cardiovascular disease and increased risk of accidents caused by daytime sleepiness. Among Norwegians 30-65 yrs, the prevalence of OSA are estimated to 16%. The golden standard in OSA-treatment is Continuous Positive Airway Pressure (CPAP). This is effective and must be used for life. However, CPAP-treatment might be uncomfortable for the patient, with poor compliance as a result. An alternative is Mandibular Advancing Splints (MAS), which is perceived as less troublesome and may initiate higher compliance. Through mapping of patient characteristics, the researchers investigate which patient-type benefits most from two different treatment-devices. The aim of the study is to assess how the MAS treatment differ from the CPAP treatment in respect to efficacy, compliance and impact on health related quality of life among patient diagnosed with mild/moderate OSA. All OSA patients referred to the Ear- Nose- Throat-department (ENT) at University Hospital, Northern-Norway (UNN) and St.Olavs Hospital were invited to participate in the study. The sample size at completion of the study should be 140 patients. Participants in the trial were randomly allocated to the two treatment groups, and assessed after 4 and 12 months of treatment. Data were collected through anamnesis, clinical examination, clinical photos, radiographs and questionnaires concerning general health related quality of life (SF36), oral health, cognitive aspects (HADS), sleep quality (PSQI), daytime sleepiness (Epworth's Sleepiness scale) and compliance.