Growing concern about mental health disorders has become a major public issue in South Korea, driven by sociocultural and economic pressures and reflected in the nation’s highest suicide rate among OECD countries. Obstructive sleep apnea (OSA), a prevalent sleep-related breathing disorder, may exacerbate psychological distress by disrupting sleep quality.This study aimed to examine the relationship between OSA risk, as measured by STOP-BANG, and mental health outcomes, including anxiety and depressive symptoms, using nationwide data from the 2021 Korea National Health and Nutrition Examination Survey (KNHANES).A total of 3,910 adults aged ≥40 years (1,706 men and 2,204 women) from KNHANES 2021 were analyzed. Participants completed the STOP-BANG questionnaire to assess OSA risk and the Generalized Anxiety Disorder-7 (GAD-7) scale to measure anxiety symptoms. Demographic, lifestyle, and clinical covariates were included, such as age, BMI, socioeconomic factors, comorbidities, and perceived stress. Logistic regression analyses were performed to examine associations between STOP-BANG scores and mental health outcomes, adjusted for potential confounders.Men exhibited higher BMI and cardiometabolic comorbidities, while women had higher rates of depressive symptoms and lower socioeconomic status (p<0.05). Higher STOP-BANG scores were significantly associated with increased perceived stress (OR 1.37, 95% CI 1.22–1.54), greater GAD-7 scores (OR 1.08, 95% CI 1.05–1.11), and higher odds of experiencing a depressive mood lasting more than two weeks (OR 1.94, 95% CI 1.54–2.45). Sex-specific analyses revealed that certain OSA risk components (e.g., snoring, tiredness, observed apnea) were more strongly associated with mental health outcomes in one gender than the other.Our findings underscore the complex interplay between sleep apnea risk factors and mental health, highlighting the need for gender-specific approaches in managing patients with potential OSA. The differential impact of OSA risk factors on mental health outcomes between genders emphasizes the importance of considering gender in both the screening and treatment of sleep apnea and associated mental health conditions.Higher OSA risk assessed by STOP-BANG was significantly associated with anxiety, stress, and depressive symptoms, independent of major confounders. The findings underscore the need for gender-specific strategies and early screening for OSA as part of comprehensive mental health assessment.