Abstract Context The association between hypothyroidism and sleep apnea (SA) has been studied, but results are conflicting and based mostly on small studies. Objective To determine whether there is a positive association between hypothyroidism and SA in the US population. Design Cross-sectional study. Setting US National Health and Nutrition Examination Survey, 2007–2008. Participants We included all subjects ≥18 years old who met inclusion criteria. Participants not on antithyroid medication with a TSH >5.6 mIU/L and those on thyroid hormone replacement regardless of TSH were categorized as hypothyroid. Participants not on thyroid hormone replacement or antithyroid medication who had a TSH ≥0.34 and ≤5.6 mIU/L were categorized as euthyroid. The diagnosis of SA was based on participants’ response when asked whether they had been diagnosed with SA by their doctors. Main Outcome Measures Multivariate logistic regression analyses were performed to determine the association between hypothyroidism and SA. Results A total of 5515 adults were included for data analysis. The prevalence of hypothyroidism and hyperthyroidism was calculated at 9.47% and 1.19%, respectively. Multivariate logistic regression analysis adjusted for demographics, health care access, body mass index, socioeconomic factors, alcohol use, smoking, and other comorbidities demonstrated a significant association between hypothyroidism and SA (OR = 1.88, 95% CI, 1.24 to 2.84, P < 0.01). Conclusion Hypothyroidism is associated with SA after adjustment for potential confounding variables.