Background: In the treatment of obstructive sleep apnea (OSA), mandibular advancing devices (MAD) are usually individually fabricated on plaster casts of both jaws from polymethyl-methacrylate. The potential disadvantages of these devices are (1) the costs and (2) the time required to construct the device. Objective: In this study, the efficacy and feasibility of a cheap MAD consisting of thermoplastic material (SnorBan^®), which can be directly moulded intraorally, were evaluated. Methods: In a prospective study, the effect of an MAD consisting of thermoplastic material was investigated in 22 consecutive patients with OSA [respiratory disturbance index (RDI) 32.6 ± 18.4/h]. Polysomnographic sleep was recorded prior to treatment and after 3 months of treatment with the MAD. Results: Three of the 22 patients who did not tolerate the MAD were excluded from the analysis, whereas 11 patients were classified as responders. In the responder group, the mean RDI decreased from 27.6 ±7.3 to 7.3 ± 2.9 (p < 0.01), correspondingly the sleep quality and the Epworth Sleepiness Scale improved (p < 0.05). Eight patients proved to be non-responders without relevant changes for the measured parameters. Conclusions: In 50% (11 of 22) of the patients, the MAD improved the OSA to a clinically relevant degree. In contrast to the majority of established MAD, the MAD investigated is cheap and immediately adaptable and thus a feasible strategy to ‘screen’ the efficacy of this therapeutic principle. Thus the construction of unnecessary MAD is avoided.