['Dysfunction of the upper esophageal sphincter (UES) is a common cause of oral-pharyngeal dysphagia (OPD). Dilation is a primary treatment, although current techniques are subject to a high rate of failure and recurrence. Devices available for UES dilation are cylindrical and were designed to distend the round lumen of the esophagus. Our objective was to determine the cross-sectional dimension of the UES in an ovine model of OPD and compare it with that of the cervical esophagus.', 'Prospective cadaveric animal study.', 'Three-dimensional casts of the upper aerodigestive tract of 10 fresh cadaveric ewes were constructed using a platinum-cured liquid silicone polymer. Cross-sections at the level of the UES and cervical esophagus were digitized and mathematically compared using geometric morphometric shape analysis.', 'Consensus shape among all 10 animals revealed that the narrowest region of the maximally distended UES has a cross-sectional shape that resembles a kidney, whereas the cervical esophagus approximates a circle. The shape of the UES and cervical esophagus were significantly different (P < .0001), and surface area calculations demonstrated that an inscribed circle significantly underestimated the area implied by the kidney-shaped UES model.'] Does geometric morphometric shape analysis in an ovine model confirm that the upper esophageal sphincter is not round?