Objective:To examine the associations of self-efficacy and outcome expectancy with adherence to continuous positive airway pressure (CPAP) therapy among Japanese men with obstructive sleep apnea (OSA) using objective adherence data for CPAP therapy.Methods:We conducted a retrospective study of 497 Japanese men with OSA who were receiving CPAP therapy. Good adherence was defined as CPAP use of ≥4 hours per night for ≥70% of nights. Logistic regression models were used to calculate odds ratios (ORs) and 95% confidence intervals (CIs) for the associations of good adherence to CPAP therapy with self-efficacy and outcome expectancy (measured with the CPAP Self-Efficacy Questionnaire for Sleep Apnea in Japanese). The models were adjusted for age, duration of CPAP therapy, body mass index, apnea–hypopnea index, Epworth Sleepiness Scale score, and comorbidities (diabetes mellitus and hypertension).Results:In total, 53.5% of participants had good adherence to CPAP therapy. The mean CPAP use was 5.18±1.53 hours/night. After adjusting for related factors, we found significant associations of good adherence to CPAP therapy with self-efficacy scores (OR, 1.10; 95% CI, 1.05–1.13;p<0.001) and outcome expectancy scores (OR, 1.10; 95% CI, 1.02–1.15;p=0.007).Conclusions:Our results indicate that self-efficacy and outcome expectancy are associated with good adherence to CPAP therapy among Japanese men with OSA.