Sleep-related breathing disorders such as snoring and obstructive sleep apnoea syndrome are the cause of significant social disruption and hypersomnolence. Several intraoral appliances for the treatment of these disorders have been described, especially where nasal continuous positive airway pressure is poorly tolerated. Mandibular Advancement Splints, such as the Herbst splint used in this study can also be offered to patients with mild to moderate sleep apnoea and simple snorers. The success and compliance rate noted in the literature are quite diverse. Few side-effects have been reported. We therefore undertook this study to assess: (1) the compliance; (2) the effectiveness; and (3) the side-effects in the long- and short-term. All patients for whom a Herbst splint had been prescribed in the last 18 months were sent a postal questionnaire regarding the above mentioned issues. In all, 179 questionnaires were posted and on analysis of the 132 returned it was noted that 82% of splints were worn and 88% of patients found the device to be effective. The long-term side-effects were minimal. In addition objective assessment on 10 patients with and without a jaw-retaining device was also obtained. We conclude that the Herbst Mandibular Advancement Splint is a justifiable option in selected subjects with sleep-related breathing disorders.