The duration of gastric acidity may affect the interpretation of esophageal pH monitoring study. The aim of this study was to increase the sensitivity of pH monitoring by simultaneous gastric and esophageal pH recording. Fifty-seven patients were enrolled in the study. After the first analysis, the recording periods in which gastric pH was >4 were excluded and after this exclusion parameters were recalculated. Of the 57 patients, 14 (24.6%) (mean age, 70+/-4.6 years) were diagnosed as having gastroesophageal reflux disease with the use of conventional method. After correction, gastroesophageal reflux disease diagnosis was made in 6 additional patients (mean age, 2.4+/-2.4 years) and total number of patients with reflux increased to 20 (35.1%) (p=0.031). The mean percentage time of gastric pH>4 was significantly greater in children younger than 2 years of age than that in those older than 2 years of age (50.6%+/-15.2% vs 33.7%+/-18.1%) (p=0.001). Exclusion of periods in which gastric pH>4 affected the results more obviously in patients younger than 2 years. Simultaneous gastric and esophageal pH monitoring is useful for the diagnosis of gastroesophageal reflux disease, particularly in children younger than 2 years of age.