Background: Obstructive sleep apnea (OSA) is a strong and independent risk factor for the development of hypertension, particularly resistant hypertension, and cardiovascular diseases. Patients with resistant hypertension have a high prevalence of OSA in association with elevated aldosterone levels, high salt intake, and salt-sensitive BP. The objective of this study was to determine whether dietary salt and aldosterone are associated with severity of OSA in patients with resistant hypertension. Methods: Ninety-seven patients with resistant hypertension were prospectively evaluated by overnight polysomnography and 24-h urinary sodium and aldosterone levels while maintaining their usual diet. Hyperaldosteronism was defined as a plasma renin activity of < 1 ng/mL/h and urinary aldosterone level of ≥ 12 μg/24 h. Results: Overall, patients' mean clinic BP was 156.3 ± 22.4/88.9 ± 13.3 mm Hg while taking an average of 4.3 ± 1.1 antihypertensive medications. Prevalence of OSA was 77.3%. Twenty-eight (28.9%) patients had hyperaldosteronism. Urinary sodium level was an independent predictor of severity of OSA only in patients with hyperaldosteronism. Conclusions: The findings suggest that dietary salt is related to the severity of OSA in patients with resistant hypertension and hyperaldosteronism. The results support dietary salt restriction as a treatment strategy for reduction of OSA severity in these patients. © 2013 American College of Chest Physicians.