Nowadays oral appliance therapy is recognised as an effective therapy for many patients with primary snoring and mild to moderate obstructive sleep apnoea (OSA), as well as those with more severe OSA who cannot tolerate positive airway pressure (PAP) therapies. For this reason, it is important to focus on objective criteria to indicate which subjects may benefit from treatment with a mandibular advancement device (MAD). Various anthropometric and polysomnographic predictors have been described in the literature, whereas there are still controversies about the role of drug-induced sleep endoscopy (DISE) and advancement bimanual manoeuvre as predictor factors of treatment outcome by oral device. Herein, we report our experience in treatment of mild moderate OSA by oral appliance selected by DISE. We performed a single institution, longitudinal prospective evaluation of a consecutive group of mild moderate patients with obstructive sleep apnoea syndrome who underwent DISE. During sleep endoscopy, gentle manoeuvre of mandibular advancement less than 5 mm was performed. In 30 of 65 patients (46.2%) we obtained an unsuccessful improvement of airway patency whereas in 35 of 65 patients (53.8%) the improvement was successful and patients were considered suitable for oral device application. Because 7 of 35 patients were excluded due to conditions interfering with oral appliance therapy, we finally treated 28 patients. After 3 months of treatment, we observed a significant improvement in the Epworth medium index [(7.35 ± 2.8 versus 4.1 ± 2.2 (p < 0.05)], in mean AHI [(21.4 ± 6 events per hour versus 8.85 ± 6.9 (p < 0.05)] and in mean ODI [(18.6 ± 8 events per hour to 7 ± 5.8 (p < 0.05)]. We observed that the apnoea/hypopnoea index (AHI) improved by up to 50% from baseline in 71.4% of patients selected after DISE for MAD therapy. In the current study, mandibular advancement splint therapy was successfully prescribed on the basis not only of severity of disease, as determined by the subject’s initial AHI, but also by DISE findings combined with results of gentle mandibular advancement manoeuvre allowing direct view of the effects of mandibular protrusion on breathing spaces in obstruction sites, and showing good optimisation of selection of patients for oral device treatment. © 2015, Pacini Editore S.p.A. All rights reserved.