Objective: To investigate the long-term efficacy and safety of oral appliances (OAs) in treating obstructive sleep apnea-hypopnea syndrome (OSAHS) by length of treatment. Materials and Methods: This is a retrospective study to review the usage of OAs in Chinese OSAHS patients in recent decades. Ninety-four valid questionnaires were returned by 412 patients with OSAHS receiving OA treatment. Among the wearers, 22 agreed to follow-up polysomnography, and 25 agreed to follow-up cephalograms. Tolerance and side effects of OAs were assessed by a survey. Comparisons of efficacy were carried out between the initial and follow-up polysomnography measurements. Cephalometric analysis was used to investigate skeletal and occlusal changes to determine safety of the OAs. Results: The longest treatment extended to 147 months, with a median of 74 months (first and third quartiles, 30 and 99 months, respectively). Among the participants, 14.9% had been treated for more than 120 months. Side effects were temporary and relatively minimal and included tooth soreness (37.2%), dry mouth (33.0%), odd bite feeling (31.9%), and excess salivation (30.8%). Polysomnography proved that OAs remained effective for the treatment of OSAHS in the long term; initial Apnea-Hypopnea Index values were reduced from a median of 24.50 (quartiles, 14.65, 54.05) without the OA to 7.40 with the OA (2.12, 10.00), and follow-up median values were 25.55 without the OA (11.71, 43.65) and 4.25 with the OA (1.38, 7.70). Cephalometric analysis indicated mild and slow changes in the skeleton and occlusion after average treatment duration of 5 years. Conclusion: OAs provided effective and safe long-term therapy for patients with OSAHS. Followup supervision is recommended since long-term alterations take place, although these appear to be minimal.