Introduction: Mandibular advancement device (MAD) may represent a feasible choice in the treatment of obstructive sleep apnea-hypopnea syndrome (OSAHS), in well selected patients. Objective: The aim of this study is to assess the efficacy of MAD in patients with OSAHS, using split night polysomnography (SNP) Method: We performed an auto controlled clinical trial to assess the efficacy of MAD in 30 patients with snoring and OSAHS. Clinical evaluation was made every 2 weeks to adjust treatment and observe changes in clinical symptoms. Three-months after placement of the MAD, a SNP was performed, using the MAD in the second half of the night, in order to compare the respiratory results. Results: SNP show significant changes with use of MAD (p<0.05) such as: Decrease in Snore index (from 159.95 to 32.46/h) and in Apnea-hypopnea index (AHI, from 22.45 to 4.63/h), increase in oxygen saturation (SaO2, from 89.98% to 91.39%) and somnolence improvement, using the Epworth Sleepiness Scale (from 14.4 to 4.6 points). Conclusion: Our data supports that the use of MAD is an alternative in the management of OSAHS, in well selected patients, used in a multidisciplinary fashion, and evaluated using a SNP.