Aims: To evaluate the influence of an oral appliance on morning headache and orofacial pain in subjects without reported sleep-disordered breathing (SDB). Methods: Twelve subjects aged 27.6 ± 2.1 (mean ± SE) years and suffering from frequent morning headache participated in this study. Each subject was individually fitted with a mandibular advancement appliance (MAA). The first two sleep laboratory polygraphic recording (SLPR) nights were for habituation (N1) and baseline (N2). Subjects then slept five nights without the MAA (period 1: P1), followed by eight nights with the MAA in neutral position (P2), ending with SLPR night 3 (N3). Subjects then slept five nights without the MAA (P3), followed by eight nights with the MAA in 50% advanced position (P4), ending with SLPR night 4 (N4). Finally, subjects slept 5 nights without the MAA (P5). Morning headache and orofacial pain intensity were assessed each morning with a 100-mm visual analog scale. Repeated measures ANOVAs and Friedman tests were used to evaluate treatment effects. Results: Compared to the baseline period (P1), the use of an MAA in both neutral and advanced position was associated with a >= 70% reduction in morning headache and >= 42% reduction in orofacial pain intensity (P = .001). During the washout periods (P3 and P5), morning headache and orofacial pain intensity returned to close to baseline levels. Compared to N2, both MAA positions significantly reduced (P .05) rhythmic masticatory muscle activity (RMMA). Conclusion: Short-term use of an MAA is associated with a significant reduction in morning headache and orofacial pain intensity. Part of this reduction may be linked to the concomitant reduction in RMMA. Keywords: mandibular advancement appliance, morning headache, oral appliance, orofacial pain, rhythmic masticatory muscle activity