To define the role of ambulatory pH monitoring in evaluating chronic cough, we studied esophageal pH values of patients referred to a gastroenterology laboratory. Chronic cough was evaluated in 31 patients, who were grouped based on response to treatments; 11 patients (35.5%) had gastroesophageal reflux (GER)-related cough, 11 (35.5%) had pulmonary/otorhinolaryngologic-related cough (1 bronchitis, 6 asthma, 2 postnasal drip, 1 pneumonia), and 9 patients (29%) had cough of unknown etiology. Esophageal pH values of groups were compared. Excessive acid reflux distally (upright and supine) and proximally (upright) and cough symptom frequency related to acid reflux were significantly higher in patients with GER. Esophageal pH monitoring had good sensitivity (91%), specificity (82%), and positive (83%) and negative (90%) predictive values in identifying GER-related cough. In summary, ambulatory pH monitoring is an excellent test for identifying patients with GER-related cough.