There is a high prevalence of gastroesophageal reflux disease (GERD) in the general population. Prevalence studies are scarce, and there is a lack of valid instruments for measuring them. The aim of this paper is to validate a questionnaire for detecting GERD. A validity study design with pathologic GERD patients and controls was used. A sample of 240 subjects age and sex paired was selected in the ratio of 3:1 (patients to controls). The initial structured questionnaire contained a variety of GERD symptoms. Internal consistency, interobserver reliability, criteria validity using 24-h esophageal pH monitoring, construct validity, and extreme group validation were assessed. Sensitivity, specificity, and predictive values were also obtained in different cutoff points of the definitive scale. A total of 180 confirmed GERD patients and 60 controls were included in the study. Mean age in years was 45 +/- 13, with no statistical difference by gender (67% were female). Internal consistency of 0.75 and interobserver reliability of 0.87 was achieved in building the scale. Extreme group validation was highly significant by assessing the scale score with 24-h esophageal pH monitoring (P <.0001). At cutoff point 3 of the scale and with a correct classification of subjects of 92.4%, sensitivity, specificity, positive, and negative predictive values were 92, 95, 98, and 79%, respectively. The conclusion of this article is that a reliable and valid instrument was built to detect GERD.