Zenker's diverticulum is thought to result from disordered coordination between the pharynx and upper esophageal sphincter. Manometric studies of the upper esophagus have been helpful in testing the hypothesis of dysmotility in the formation and growth of a Zenker's diverticulum; however, the data have provided conflicting evidence. Manometric studies show that resting upper esophageal sphincter pressure is normal in some patients with Zenker's diverticulum and decreased in others. Abnormal premature relaxation and contraction of the upper esophageal sphincter seen in some patients with Zenker's diverticulum may be accompanied by pharnygeal contractions against a closed sphincter. This abnormality is thought by some investigators to be the cause of Zenker's diverticulum, but not by others who have found normal upper sphincter relaxation. Future manometric studies will very likely elucidate the pathogenesis of Zenker's diverticulum.