With recent interest in sleep apnoea, oral devices have been proposed and used increasingly to treat patients suffering from snoring and obstructive sleep apnoea (OSA). Numerous case reports have been published and studies have been carried out to determine the efficiency and mechanism of action as well as evaluate side effects, complications and costs of different oral devices in the treatment of habitual snoring and OSA. A summary of the scientific basis and current opinions regarding oral devices in the treatment of habitual snoring and obstructive sleep apnoea is presented in this article. The selection of papers was based on a computerised search of published clinical and associated studies identified by MEDLINE from 1980 to November 2000. Although there is not yet enough scientific evidence for the clinician to determine which appliance is most likely to improve symptoms for a given patient, it appears from the literature that dental devices may have a place in the treatment of habitual snoring and mild and moderate cases of OSA. However, most of the studies are case series, raising questions on validity, and few studies use appropriate control groups. The general opinion is that these patients should not be treated without a sleep study as the OSA must be diagnosed before beginning treatment with oral devices to identify patients at risk and to provide a baseline to establish the effectiveness of the treatment. The main advantages of oral devices is the relative simplicity of the treatment, its reversibility and cost-effectiveness, and the fact that they can be used as an alternate treatment in patients who are unable to tolerate nasal continuous positive airway pressure (nCPAP) or who are poor surgical risks. Side effects occur in a significant proportion of patients using the MAD. In most cases these are minor and their importance must be balanced against the efficacy of the MAD in treating snoring and OSA. n.