Purpose: To investigate subjective efficiency outcomes after maxillomandibular advancement (MMA) surgery in obstructive sleep apnea (OSA) patients. Material and Methods: A prospective cohort study was carried out between December 2016 and May 2021, including 30 severe or treatment-refractory OSA patients treated by MMA surgery. All patients answered four validated questionnaires: the Epworth Sleepiness Scale (ESS), Functional Outcomes of Sleep Questionnaire (FOSQ), Mandibular Function Impairment Questionnaire (MFIQ), and EQ-5D-3L (i.e., EQ-5D and EQ-VAS). They also answered one custom-made questionnaire (AMCSQ). Questionnaires were requested to be filled out 1 week before surgery and at least 6 months after surgery. Results: The total preoperative and postoperative scores on the questionnaires were compared. The mean total ESS (p< 0.01), FOSQ (p< 0.01), EQ-5D (p< 0.05), and EQ-VAS (p< 0.01) scores showed significant improvement, which was in accordance with an improvement in the mean postoperative apnea/hypopnea index score (p< 0.01). In contrast, the mean total MFIQ score (p< 0.01) indicated a decline in mandibular function. Conclusion: This study confirms the hypothesis that MMA surgery in OSA patients improves outcomes, both objectively and subjectively, with the exception of postoperative mandibular function.