There is no standardized protocol for the clinical evaluation of orofacial components and functions in patients with obstructive sleep apnea. The aim of this study was to examine the validity, reliability, and psychometric properties of the Expanded Protocol of Orofacial Myofunctional Evaluation with Scores (OMES-expanded) in subjects with obstructive sleep apnea. Patients with obstructive sleep apnea and control subjects were evaluated, and the validity of OMES-expanded was tested by construct validity (i.e. the ability to discriminate orofacial status between apneic and control subjects) and criterion validity (i.e. correlation between OMES-expanded and a reference instrument). Construct validity was adequate; the apneic group showed significantly worse orofacial status than did control subjects. Criterion validity of OMES-expanded was good, as was its reliability. The OMES-expanded is valid and reliable for evaluating orofacial myofunctional disorders of patients with obstructive sleep apnea, with adequate psychometric properties. It may be useful to plan a therapeutic strategy and to determine whether the effects of therapy are related to improved muscle and orofacial functions.