Several studies have reported that sleep bruxism rarely occurs in isolation. Recently, in an epidemiological study of sleep bruxism and risk factors in the general population, it was found that among the associated sleep symptoms and disorders obstructive sleep apnea (OSA) was the highest risk factor for tooth grinding during sleep. The purpose of this report was to evaluate the effect of continuous positive airway pressure (CPAP) on sleep bruxism in a patient with both severe OSA and sleep tooth grinding. Two polysomnographic (PSG) recordings were carried out. The first showed 67 events of sounded tooth grinding, most of them appearing as an arousal response at the end of apnea/hypopnea events in both the supine and lateral postures. During the CPAP titration night most breathing abnormalities were eliminated and a complete eradication of the tooth grinding events was observed. The results of this study suggest that when sleep bruxism is related to apnea/hypopneas, the successful treatment of these breathing abnormalities may eliminate bruxism during sleep.