The prevalence of gastroesophageal reflux after successful pneumatic dilatation was investigated in 30 patients with primary esophageal motor disorder. After a median follow-up period of 377 days, three patients presented symptoms of acid reflux and five patients had endoscopic esophagitis (grade I, 3 patients; grade II, one patient; and grade III, one patient). Ambulatory 24 hr. esophageal pH monitoring was positive in 20% and 30% of the patients compared to our normal values and to those from other series from the literature, respectively. The concordance between pH results and symptoms and/or endoscopic esophagitis was very low. It is concluded that 24 hr. esophageal pH monitoring is frequently abnormal after pneumatic dilatation, but its clinical significance is low, because very few patients have symptoms and/or severe esophagitis.