A mandibular advancement splint (MAS) may be an alternative treatment for snoring and obstructive sleep apnoea (OSA). However, there is little subjective or objective information concerning long-term effectiveness, compliance and side effects. A retrospective questionnaire was used to survey these issues plus patient satisfaction and maintenance requirements in 166 patients who could have worn a mandibular advancement splint for over a year. One-hundred and twenty-six (76%) subjects returned the questionnaire, (84 with OSA, 42 snorers), of whom 69 (55%) reported still using the splint regularly, 47 (37%) every night. The most common reported reasons for stopping use were discomfort (29/ 57; 52%) of nonusers), and poor perceived efficacy (12 subjects). Users reported more daytime symptoms, and they and their partners were more likely to observe improvements with splint use. Side effects were reported by 49 subjects, more commonly in nonusers. Sixty-five of 67 current users and 23 of 41 nonusers reported less snoring with splint use (p = < 0.001). Long-term mandibular advancement splint usage appeared less satisfactory than previously reported, however, splints were considered effective by 97% of current users and even by over half of those who had stopped use. Reasons for stopping use included side effects, social circumstances, dental treatment, as well as lack of perceived efficacy.