Objective: To assess the clinical value of trans-abdominal ultrasonography for the diagnosis of achalasia. Methods: The subjects were divided into 3 groups, with 8 patients suffering from achalasia as the patient group, 10 normal individuals and 8 patients with cardiac carcinoma as controls. Real-time trans-abdominal ultrasonography (TAUS) was employed to investigate the lower esophagus and cardia of all subjects through water provocative test, and the sonographic findings were compared. After treated by administration of drugs, pneumatic balloon dilation or intrasphincteric injection of botulinum toxin, the 8 patients with achalasia were re-examined by TAUS for longitudinal comparison. Results: (1) The normal subjects had no dilation of cardia and lower esophagus before drinking water, but their cardias opened rapidly in accordance with the drinking action to allow water enter the stomach. (2) All the patients with achalasia were found to have dilation of lower esophagus before taking water. During a 10-min continuous TAUS scanning, 5 patients demonstrated absence of relaxation of cardias and no passage of water from the esophagus into the stomach.The other 3 showed slight and intermittent relaxation of cardias with water flow into the stomach. Thirty minutes after water provocative test all the 8 patients had water retardation within the lower esophagus. (3)The patients with cardiac carcinoma had an ultrasound feature of enlargement of cardiac ring and thickening of cardiac wall without dilation of lower esophagus before water provocative test. Water, while being taken,passed the cardia more slowly than in normal condition. Conclusion: TAUS is a readily accepted examination on patients because they need only to drink a little water. By demonstrating the size of cardia, thickness of cardiac wall and monitoring the water flow through the cardia, TAUS can quickly give reliable diagnostic clues to achalasia. TAUS also can be used for making assessment of therapeutic effect on achalasia.