Aims: To explore whether traumatic brain injury (TBI) patients have a higher prevalence of sleep bruxism (SB) and a higher level of orofacial muscle activity than healthy controls and whether orofacial muscle activity in the context of mild TBI (mTBI) increases the risk for headache disability. Methods: Sleep laboratory recordings of 24 mTBI patients (15 males, 9 females; mean age ± standard deviation [SD]: 38 ± 11 years) and 20 healthy controls (8 males, 12 females; 31 ± 9 years) were analyzed. The primary variables included degree of headache disability, rhythmic masticatory muscle activity (RMMA) index (as a biomarker of SB), and masseter and mentalis muscle activity during quiet sleep periods. Results: A significantly higher prevalence of moderate to severe headache disability was observed in mTBI patients than in controls (50% vs 5%; P = .001). Although 50% and 25% of mTBI patients had a respective RMMA index of ≥ 2 episodes/hour and ≥ 4 episodes/hour, they did not present more evidence of SB than controls. No between-group differences were found in the amplitude of RMMA or muscle tone. Logistic regression analyses suggested that while mTBI is a strong predictor of moderate to severe headache disability, RMMA frequency is a modest but significant mediator of moderate to severe headache disability in both groups (odds ratios = 21 and 2, respectively). Conclusion: Clinicians caring for mTBI patients with poorly controlled headaches should screen for SB, as it may contribute to their condition. Keywords: headache, polysomnography, rhythmic masticatory muscle activity, sleep bruxism, traumatic brain injury