The rumination syndrome is defined as a process in which a person chews regurgitated gastric contents and then either partially ejects or swallows them. We report 12 cases of rumination in which the clinical diagnosis was supported by esophageal and gastrointestinal motility studies. These patients showed a characteristic pressure spike-wave pattern that was associated with regurgitation and was recorded simultaneously at all manometric sites. These spike waves increased significantly in frequency (p less than 0.001) and amplitude (p less than 0.04) during the postprandial period. The underlying gastrointestinal motility was normal except for a small decrease in postprandial antral motility index, with mean (+/- SE) values of 13.2 +/- 0.3 for patients compared with 14.2 +/- 0.3 for eight healthy adult controls (p less than 0.03). Nine patients had significant personality disturbances, including six whose scores on the Minnesota Multiphasic Personality Inventory for hypochondriasis and depression were significantly above the reference population (p less than 0.02). The rumination syndrome should be considered in adult patients with long-standing postprandial vomiting. The manometric pattern is characteristic.