Mandibular advancement device (MAD) has been described as an alternative treatment to the severe obstructive sleep apnea (OSA), once it is not as effective as the continuous positive airway pressure therapy (CPAP) in reducing the apnea and hypopnea index (AHI). The objective of this study is to report a case using a MAD in a CPAP-intolerant patient suffering from severe OSA. Polysomnography exams were performed before and after treatment. Five months after fitting and titrating the MAD, the AHI was reduced from 80.5 events/hour to 14.6 events/hour and the minimum oxyhemoglobin saturation (SpO2) increased from 46% to 83%. A two-year assessment of therapy revealed an AHI of 8 events/hour and SpO2 of 85%.