Abstract: To evaluate the diagnostic efficacy anatomical measurements of distal esophagus by ultrasonography in diagnosis of gastroesophageal reflux in children. All children suspicious to Gastroesophageal Reflux Disease (GERD) according to clinical history and physical examination who were indicated for further studiy with endoscopy and esophageal biopsy (as the gold standard) and without known history or current ulcer were considered to enter the study. An ultrasonographic study (3.5 MHz probe (Aloka1700, Japan)) did for all patients and 6 anatomical parameters (including the esophageal diameter, esophageal wall thickness, esophageal mucosal thickness, hiatal diameter, subdiaphragmatic esophageal length and gastric wall thickness) were measured in the ultrasound. Then the patients underwent an upper gastrointestinal endoscopy and esophageal biopsies were taken. The histopathologic criteria for GERD were erythema, ulcer, barret esophagus and leukocyte infiltration. According to the sonographic and histopathologic results, for all measurements, we plotted the receiving operative characteristics (ROC) curve to assess the area under the curve (AUC) as an indicator for diagnostic efficacy. For the best variables, we selected cut off points and then calculated the diagnostic indices (including sensitivity, specificity, positive and negative redictive values). Totally 103 (57 patients (mean age of 4.7±3.5 years) and 46 controls (mean age of 5.2±3.9 years)) entered the study. The mean esophageal diameter was 12±2.7 mm (6-17) in patients and 10.1±2.4 in controls; the mean sub diaphragmatic esophageal length was 15.9±6.3 mm in patients and 22.2±9.9 in controls (both p<0.0001). Except for Gastric wall thickness, other sonographic measures were statistically greater in patients (all Ps = 0.016) Computing AUC of 6 variables revealed all of them are equal or >0.63 (all p<0.025) and the highest value was for esophageal diameter and subdiaphragmatic esophageal length (both 0.71). Dividing esophageal diameter by subdiaphragmatic esophageal length yielded a new variable that its AUC was 0.76. Considering a cut-off point equal to 7 mm for esophageal diameter yielded a sensitivity of 0.96 while for cut-off point of 14.5 yielded a specificity of one. Considering a cut-off point equal to 10 mm for subdiaphragmatic esophageal length yielded a specificity of 0.93 while for cut-off point of 0.3 yielded a sensitivity of 0.98. Considering a cut-off point equal to 7 mm for esophageal diameter divided by subdiaphragmatic esophageal length yielded a sensitivity of 1, while for cut-off point of 1.5 yielded a specificity of 0.96.