© Medicina Oral S. L. C.I.F.Background: Despite the advances in the treatment of obstructive sleep apnea (OSA) with mandibular advancement appliances (MAA), their effectiveness is dependent on the patients’ compliance. Our aims were to evaluate the long-term adherence to MAA therapy and patients’ experiences of the treatment in OSA. Material and Methods: Sixty-nine patients (52 males, 17 females; Mean age: 54.4±10.8 years) were included in the study. The subjects were mild (56%) and moderate (44%) OSA patients who had been treated using MAA at least 4 years prior to the study. A phone survey was used to determine the demographic characteristics of the patients, as well as to assess self-reported adherence to therapy, subjective long-term effectiveness, and patient experiences with the appliance. Descriptive statistics, Pearson Chi-square test, and independent samples t-test were used for data analysis. Results: Only 22 (32%) patients reported using the appliance regularly. Most of the non-adherent patients had stopped using their appliances in the first year (55%). The mean duration of appliance use was 33.5 months (Me-dian: 12 months). No significant differences in appliance type, OSA severity, educational level, gender, marital status, income status, employment status or place of residence existed between adherent and non-adherent subjects. Adherent subjects were significantly younger than non-adherent subjects (Age: 50.6 ± 11.9 versus 56.1 ± 9.9, p < 0.05). The most common reasons reported by patients were inability to adapt to the appliance (62%) and pain in the temporomandibular joint (38%). The most common factors associated with continued usage were effectiveness (100%) and ease of use (64%). Conclusions: The overall long-term nonadherence to MAA therapy in mild-to moderate OSA patients was high suggesting that barriers to MAA therapy adherence should be prevented to increase the efficiency of oral appliance treatment in OSA and achieve better outcomes for this disease.