OBJECTIVE: Upper airway resistance syndrome is a sleep-disordered breathing syndrome that is characterized by repetitive arousals resulting in sympathetic overactivity. We aimed to determine whether upper airway resistance syndrome was associated with poorly controlled hypertension. METHODS: A total of 40 patients with resistant hypertension were enrolled in the study. All of the patients underwent polysomnographic examinations and 24-hour ambulatory blood pressure monitoring to exclude white coat syndrome and to monitor treatment efficiency. Among 14 upper airway resistance syndrome patients, 2 patients had surgically correctable upper airway pathologies, while 12 patients were given positive airway pressure therapy. RESULTS: All patients underwent polysomnographic examinations; 22 patients (55%) were diagnosed with obstructive sleep apnea and 14 patients (35%) were diagnosed with upper airway resistance syndrome, according to American Sleep Disorders Association criteria. The patients with upper airway resistance syndrome were younger and had a lower body mass index compared with other patients, while there were no difference between the blood pressure levels and the number of antihypertensive drugs. The arousal index was positively correlated with systolic blood pressure level (p = 0.034; rs = 0.746), while the Epworth score and AHI were independent of disease severity (p = 0.435, rs = 0.323 and p = 0.819, rs = -0.097, respectively). Eight patients were treated with positive airway pressure treatment and blood pressure control was achieved in all of them, whereas no pressure reduction was observed in four untreated patients. CONCLUSIONS: We conclude that upper airway resistance syndrome is a possible secondary cause of resistant hypertension and that its proper treatment could result in dramatic blood pressure control.