Aims: To evaluate the prevalence of pain associated with temporomandibular disorders (TMD) in obstructive sleep apnea syndrome (OSAS) patients referred for oral appliance therapy. Methods: Eighty-seven patients (46 men and 41 women), between 18 and 65 years of age, with an apnea-hypopnea index (AHI) of > 5 and 30 (events by sleep hour), and body mass index (BMI) of = 30 Kg/m2 were evaluated according to the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) to determine the presence of signs and symptoms of TMD. Statistical analyses included correlations assessed by Pearson's test. Results: Fifty-two percent of patients presented symptoms of TMD. Thirty-two patients (average age 47 ± 11 years, AHI 17.3 ± 8.7, BMI 25.9 ± 3.8 kg/m2) completed the study. According to the Scoring Protocol for Graded Chronic Pain (Axis II-RDC/TMD), 75% of the patients presented chronic pain related to TMD, categorized as low disability grade I ( 50 points for pain intensity, and 3 disability points). The most common TMD diagnosis was myofascial pain with and without limited mouth opening and arthralgia (50%). Conclusion: The high prevalence of TMD in the current study indicates that patients with OSAS referred for oral appliance therapy require specific evaluation related to TMD. Keywords: oral appliance, prevalence, side effects, sleep apnea, temporomandibular disorders