Obstructive sleep apnea (OSA) is defined as a sleep-related breathing disorder characterized by partial or complete obstruction of the upper airway during sleep, leading to breathing pauses and oxygen desaturation. There is a connection with myofunctional disorders, as they may contribute to the onset or worsening of OSA due to weakness or dysfunction of the muscles responsible for airway patency, nasal breathing, and swallowing. This chapter focuses on the methods and procedures used to diagnose myofunctional disorders (related to the muscles and function of the oral cavity, tongue, and respiratory muscles) in patients suffering from obstructive sleep apnea (OSA). The aim of this document is to establish a basis for conducting an initial clinical examination to identify general orofacial dysfunctions while providing specific tools for a more detailed understanding of these issues. A systematic, structured, and comprehensive evaluation enables the diagnosis and prognosis of myofunctional imbalances and their influence on the oral cavity and in obstructive sleep apnea.