Objectives: Obstructive sleep apnea (OSA) is associated with treatment-resistant hypertension (RHTN) and may contribute to refractory hypertension (RfHTN). The objective of the current study was to test the hypothesis that patients with RfHTN have more severe OSA compared with patients with controlled RHTN. Methods: Patients (n=187) referred to the University of Alabama at Birmingham Hypertension Clinic for evaluation and treatment of RHTN, defined as uncontrolled blood pressure (BP) (SBP-130mmHg or DBP-80 mmHg) despite the use of at least three antihypertensive medications including a diuretic, were enrolled following completion of at least three follow-up clinic visits. RfHTN was defined as uncontrolled high BP despite treatment with five or more antihypertensive agents of different classes, including a long-acting thiazide-type diuretic and a mineralocorticoid receptor antagonist. Following enrollment, all patients (n=130) completed 24-h ambulatory BP measurement and overnight diagnostic polysomnography during normal nightly use of continuous positive airway pressure. Analyses examined the severity of OSA and related sleep characteristics among patients with RfHTN versus controlled RHTN. Results: Of the 130 evaluated patients, 37 (28.5%) had RfHTN and 93 (71.5%) had controlled RHTN. In unadjusted analyses, there was not a significant difference in OSA severity, oxygen saturation, or hypoxemia time in patients with RfHTN versus controlled RHTN (P>0.05). Men with RfHTN had more severe OSA compared with men with controlled RHTN (P=0.044). In adjusted analyses, OSA severity was associated with sex (P<0.0001), but not hypertension phenotype (P=0.17). Conclusion: The severity of OSA may contribute to RfHTN status in men but not women.