Aims: To determine the prevalence of sleep bruxism (SB) in adult obstructive sleep apnea (OSA) patients, to assess the association between SB and OSA in terms of sleep macrostructure and respiratory parameters, and to determine possible OSA risk factors for SB. Methods: Type I polysomnographic data of 147 adult OSA patients (mean age 44.6 ± 12.8 years) were evaluated for SB. SB episodes were scored when masseter rhythmic masticatory muscle activity (RMMA) was twice the background electromyography amplitude, and SB was established when patients had more than four SB episodes per hour of sleep. Demographic characteristics, sleep macrostructure, and respiratory parameters, including respiratory-related arousal index (RAI), spontaneous arousal index (SAI), oxygen desaturation index (ODI), and Apnea-Hypopnea Index (AHI), were analyzed for differences between patients with and without SB using independent samples t test and Mann-Whitney U test. Multivariate logistic regression analysis was performed to determine the odds of OSA risk factors for SB. Results: Approximately one-third (33.3%) of the adult OSA patients had concomitant SB. Most of the RMMA observed in OSA-SB patients was phasic in nature. OSA patients with SB demonstrated significantly greater RAI (P = .001) and ODI (P = .005). RAI (odds ratio =1.05, 95% confidence interval = 1.00 to 1.10) and SAI (odds ratio = 0.89, 95% confidence interval = 0.80 to 0.96) demonstrated marginal effects on the odds of experiencing SB. Conclusion: About one-third of adult OSA patients had SB, and these patients demonstrated significantly more respiratory-related arousals and oxygen desaturations. These findings suggest that a phenotypic subtype of OSA patients with predominantly phasic SB exists and allude to a possible protective role of RMMA in respiratory-related arousals. Schlagwörter: association, bruxism, obstructive sleep apnea