BACKGROUND/AIMS: There have been controversies on whether IEM is the marker for pathologic acid exposure, and the relationship between the other motility disorders and pathologic acid exposure has been studied only rarely. This study was done to evaluate the relationship between esophageal motility disorders, including IEM, and pathologic acid exposure. METHODS: We retrospectively reviewed the data of 493 patients (median age: 47 years, 42% male) who had undergone both esophageal manometry and 24-hour pH monitoring within one month. Pathologic acid exposure was defined as a distal esophageal pH<4 for more than 4% of the total monitoring time, and IEM was defined as when more than 30% of the peristaltic waves were found to be ineffective. RESULTS: Esophageal motility disorders were found in 125 patients (25%) and IEM was the most frequent motility disorder (51%). Pathologic acid exposure was found in 115 patients (23%). The prevalence of pathologic acid exposure was significantly high in the patients with IEM (p=0.014). The other motility disorders did not show any significant relationship with pathologic acid exposure. When each manometry parameter was reviewed separately, only low distal body amplitude was related with pathologic acid exposure. CONCLUSIONS: Among the esophageal motility disorders, only IEM showed a significant relationship with pathologic acid exposure.