This study examined the effect of head rotation on the mechanics of swallowing in healthy subjects, as well as the effects of this postural change on the oropharyngeal swallow of five patients with lateral medullary syndrome (LMS). Videofluoroscopic studies of swallowing in the normal subjects revealed that head rotation to either side increased upper esophageal sphincter (UES) opening diameter by an average of 2mm without affecting the period of UES opening or the oropharyngeal transit time. Maximal rotation of the head to the right or left caused the bolus to lateralize away from the direction of rotation, and also caused a significant (18mmHg or 35%) fall in UES pressure. In the face forward position, the LMS patients exhibited barium residue in the pharynx and pyriform sinuses, as well as diminished UES opening diameter. The fraction of the bolus swallowed and the UES opening diameter increased significantly with the head turned toward the paretic side in the LMS patients. We conclude that head rotation can improve swallowing in patients with unilateral oropharyngeal dysphagia. Two potentially beneficial effects were observed: (1) functional exclusion of the relatively flaccid, weakened pharyngeal wall, and (2) reduced UES tone. Which of these mechanisms is operative probably depends on the dominant mechanisms of dysphagia. In individuals with substantial impairment of UES opening, head turning reduces the resistance of the sphincter that must be overcome by pharyngeal contraction. In individuals with a flaccid hemipharynx, which dissipates pharyngeal pressure, head rotation excludes these structures from the bolus path and allows pharyngeal pressure to be directed at the UES.