PURPOSE We compared transabdominal sonography with upper gastrointestinal tract x-ray series (barium study) for evaluating gastroesophageal junction disease. METHODS Fifty-five patients underwent barium study and sonography, which were performed independently by 2 radiologists. The results were compared. Normal findings were verified by esophagoscopy or by clinical follow-up; all abnormal findings were verified by biopsy, surgery, or manometry. RESULTS Findings from barium study and sonography agreed in all 30 of the normal cases. On sonography, normal gastroesophageal junctions had multiple layers of different echogenicities (mean wall thickness, 4.9 mm); the 20 cancer cases all appeared as a mass-like thickening (mean, 14.9 mm) on sonography. Barium study findings were misinterpreted as achalasia in 2 cancer cases. One benign stricture was misinterpreted as cancer by both sonography and barium study. Of the 4 cases of achalasia, 3 were revealed by sonography as normal gastroesophageal junctions with proximal dilatation. CONCLUSIONS Transabdominal sonography is useful for revealing the extramucosal component of gastroesophageal junction disease. The modality is especially useful for distinguishing between achalasia and infiltrative cancer when barium study shows smooth circumferential narrowing.