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.