['To investigate the impact of esophagogastroduodenoscopy with conscious sedation on the subsequent 24-h catheter-based pH monitoring.', 'Fifty patients with extra-esophageal symptoms of gastroesophageal reflux disease undergoing ambulatory dual-probe 24-h pH monitoring were enrolled from March 2010 to August 2011. All of the data were collected prospectively and analyzed retrospectively. Thirty-six patients (72%, group A) underwent pH monitoring shortly after esophagogastroduodenoscopy (EGD) with conscious sedation, and 14 patients (28%, group B) underwent pH monitoring without conscious sedation. The 24-h pH data from two time periods were analyzed: the first 4 h (Period I) and the remaining time of the study (Period II).', 'The mean age of the patients was 49.6 ± 12.5 years; 20 patients (40%) were men. The baseline data, including age, sex, body mass index, reflux esophagitis, the Reflux Symptom Index, and the Reflux Findings Score, were comparable between the two groups. The percentage of total time with a pH < 4 and the frequency of acid reflux during Period I\u2005were not significantly different between the two groups, as measured using both pharyngeal (0.03% ± 0.10% vs 0.07% ± 0.16%, P = 0.32; and 0.07 ± 0.23 episodes/h vs 0.18 ± 0.47 episodes/h, P = 0.33, respectively) and esophageal probes (0.96% ± 1.89% vs 0.42% ± 0.81%, P = 0.59; and 0.74 ± 1.51 episodes/h vs 0.63 ± 0.97 episodes/h, P = 0.49, respectively). The percentage of total time with a pH < 4 and the frequency of acid reflux were also not significantly different between Periods I and II in group A patients, as measured using both pharyngeal (0.03% ± 0.10% vs 0.23% ± 0.85%, P = 0.21; and 0.07 ± 0.23 episodes/h vs 0.29 ± 0.98 episodes/h, P = 0.22, respectively) and esophageal probes (0.96% ± 1.89% vs 1.11% ± 2.57%, P = 0.55; and 0.74 ± 1.51 episodes/h vs 0.81 ± 1.76 episodes/h, P = 0.55, respectively).'] Does esophagogastroduodenoscopy with conscious sedation interfere with catheter-based 24-h pH monitoring?