ObjectivesThis study assessed the effects of obstructive sleep apnea (OSA) on mental health, health-related quality of life (HRQoL), and multimorbidity in Korean adults.MethodsThe study included 8030 participants from the Korea National Health and Nutrition Examination Survey Ⅷ (2019–2020). The risk of OSA was assessed using STOP-BANG questionnaire. Depression was measured using the Patient Health Questionnaire-9 (PHQ-9), and stress was measured using a questionnaire. HRQoL was determined by EuroQol 5-dimension (EQ-5D) and Health-related Quality of Life Instrument with 8 Items (HINT-8) scores. Multimorbidity was defined as the presence of 2 or more chronic diseases. A complex sample multivariate logistic regression analysis was conducted.ResultsParticipants with a high OSA risk were more likely to a have high PHQ-9 score (OR 4.31, 95% confidence interval [CI] 2.80–6.65), total depression (OR 4.07, 95% CI 2.67–6.19) stress (OR 2.33, 95% CI 1.85–2.95), lower EQ-5D (OR 2.88, 95% CI 2.00–4.15) and HINT-8 scores (OR 2.87, 95% CI 1.65–4.98), and multimorbidity (OR 2.62, 95% CI 2.01–3.41) than participants with low OSA risk. High OSA risk was significantly associated with all EQ-5D and HINT-8 items.ConclusionsThis study adds to the few population-based studies showing associations between mental health, HRQoL, and multimorbidity using nationwide data. OSA prevention might be helpful for good mental health, improving HRQoL, and comorbidity burdens. The results provide novel insights regarding the association between sleep apnea and multimorbidity.