BACKGROUND/AIMS: Esophageal segmental dysmotility has been extensively studied, while reports regarding segmental hypotonic peristalsis are rare. This study was carried out to elucidate the possible relationship between segmental hypotonic peristalsis and midesophageal diverticulum. METHODS: Fifteen patients with midesophageal diverticulum and 15 age- and sex-matched controls were evaluated with conventional and mapping esophageal manometry. RESULTS: Conventional manometric parameters were similer in the patients and controls. The conventional manometry identified motility disorders in 5 patients (33%) (4 nonspecific esophageal motility disorders and 1 nutcracker esophagus). The mapping manometry showed that segmental hypotonic peristalsis was noted in 6 patients (40%), but it was not found among the controls. Five patients (33%) showed no abnormality from either manometric method. CONCLUSIONS: This observation suggests that segmental hypotonic peristalsis is frequently found in patients with idesophageal diverticulum, although its clinical significance and role in the pathogenesis of diverticulum remain to be investigated. Mapping manometry may be a useful tool in the cases with suspected segmental esophageal dysmotility including diverticulum, even though the conventional manometry shows normal finding.