The distribution of gas in the digestive tract is easily detected by a plain abdominal radiograph and associated with abdominal symptoms in some dyspeptic patients. Therefore, we investigate whether a gastric bubble detected on the abdominal radiograph is associated with gastroesophageal reflux diseases (GERD) symptoms or not. All of the patients were asked to respond to the F-scale questionnaire regardless of their chief complaints. Plain abdominal films in the erect position were used to classify the form of gastric bubble into four groups: dome-type, irregular-type, stomach-type and undetected-type. The gastric bubble was found in 93.4% of patients on plain films in the erect position. Of them, 55 had a dome-type gastric bubble that indicates the distended fundus and fluid levels. GERD was most frequently detected in the stomach-type group, followed by undetected-type, irregular-type and dome-type. The mean score of the F-scale was significantly higher in stomach-type than in dome-type. It is concluded that a gastric bubble detected on plain abdominal films is an informative marker for evaluating the functional disorder of upper digestive tracts. Physicians have to recognize the importance of plain films of the abdomen in the diagnostic process of GERD.