Background: Continuous positive airway pressure (CPAP) is the first line therapy for obstructive sleep apnea (OSA) but its effectiveness requires high adherence. We aimed to assess the impacts of the spouse's/partner's involvement and the quality of the couple's relationship on CPAP adherence. Methods: In a multicenter prospective study conducted in France, patients reported their subjective views regarding their partner's engagement in their CPAP treatment and the quality of their marital relationship using the Quality of Marriage Index. A hierarchical linear model was built to assess the predictors of CPAP adherence at day 120. Structural equation modeling was performed to evaluate the direct and indirect effects of the spouse's/partner's engagement and the quality of the couple's relationship on CPAP adherence. Results: The 290 OSA patients were predominantly male (77%), with a median age of 53 years IQR: [46; 62], median BMI: 32 kg/m2 [28.6; 35.9] and median apnea + hypopnea index: 43/per hour [33; 58]. Independent factors for CPAP adherence at day 120 were the partner's encouragement of CPAP usage and a stable relationship exceeding 30 years, although emotional support or collaboration were not associated with CPAP adherence. Structural equation modeling demonstrated that spouse's/partner's engagement is directly related to CPAP adherence and improvement of symptoms, and that CPAP adherence is a mediator of disease-specific health-related quality of life. Marital quality was a significant moderator of these interactions meaning that a spouse's/partner's engagement improved adherence only when the quality of marriage index was high. Conclusion: Future research and integrated OSA management should systematically include and document the role of the spouse/partner in CPAP adherence.