The effect of a dental appliance (DA) is usually evaluated in a single mandibular position reached after several weeks and corresponding to either improvement of symptoms or intolerance to any further advancement. The purpose of this study was to test the feasibility of one-night evaluation of the efficacy of a DA. The study population consisted of seven patients (six men) with obstructive sleep apnea syndrome (66.9 +/- 32.4 apneas and/or hypopneas per hour). Patients underwent two consecutive polysomnographies; first with a temporary DA (two arches connected by a hydraulic system) progressively adjusted during the night to correct sleep disordered breathing and second with a permanent DA (two arches connected by Herbst attachments) set to the effective degree of advancement during the titration night. All patients completed the protocol. The mean mandibular advancement reached during the titration night was 12.6 +/- 2.7 mm. Arousal was never observed during or for 60 seconds following advancement. The apnea-hypopnea index (AHI) was significantly reduced from 66.9 +/- 32.4 to 26.1 +/- 20.7 per hour during the titration night from the diagnostic night (p < 0.01). During the second night, the AHI was 19.6 +/- 20.2 per hour and was less than 20 per hour in 71.4% of patients and less than 10 per hour in 42.9% of patients. The efficacy of a DA can be evaluated during a single night of polysomnography.