The cricopharyngeus (CP) is a striated muscle sphincter situated at the pharyngoesophageal junction. The upper esophageal sphincter is comprised of the striated CP muscle and nonmuscular components at the level of the cricoid cartilage. This review describes the basic anatomy and physiology of the CP muscle, its central and peripheral relationship, methods of investigating it, and electrophysiological properties related to deglutition. The main function of the CP muscle is to control flow between the pharynx and esophagus. The CP sphincter muscle is tonically contracted at rest and relaxes during swallowing, belching, and vomiting. Electromyography (EMG) of the CP sphincter muscle has been undertaken frequently in a variety of subhuman species with the aim of understanding deglutition, whereas it has seldom been reported in healthy human subjects and patients. Increased knowledge of the physiology and anatomy of the human CP sphincter muscle is not only important scientifically but is necessary for advancing the diagnosis and treatment of oropharyngeal dysphagia, for which neurological causes are responsible in 80% of cases. (C) 2002 Wiley Periodicals, Inc.