The aim of this study was to characterize the motion, morphology, and pressure of the upper esophageal sphincter (UES). The UES and its surrounding structures were evaluated in seven normal subjects and four human cadavers, using simultaneous high-resolution endoluminal sonography and manometry. The UES musculature on ultrasound is a C-shaped structure with an angle of 107 +/- 19 degrees. The mean peak resting UES pressure was 74 mm Hg, with a total cross-sectional area (CSA) of 0.87 +/- 0.33 cm2. During swallowing, the UES moved in an orad direction. Localizing the UES sonographically, the peak UES pressure in the cadavers was 19.7 +/- 10.0 mm Hg. The UES has a greater muscular CSA and resting pressure than the upper esophageal body. In the cadaver studies, the UES was imaged in conjunction with a significant increase in pressure, indicating that the pressure is due to passive mechanical conformational changes.