OBJECTIVE Foregut duplication cysts are rare congenital anomalies of enteric origin found most commonly in children and rarely in adults. They are usually found in adults on routine radiological studies and represent a challenging diagnostic problem. Conventional imaging tests do not lead to a conclusive diagnosis. With endoscopic ultrasonography, it is possible to distinguish between cystic and solid masses and to accurately establish the location of the cyst in relation to the gastrointestinal wall and to the mediastinum. METHODS Seven patients who had endoscopic ultrasonography performed because of differentiation between a cystic or solid mass lesion in the chest or abdomen could not be made with conventional radiological methods are described. RESULTS In all patients, a definite diagnosis was established by endoscopic ultrasonography. The diagnosis was confirmed in 2 patients after surgical excision. CONCLUSIONS Surgery can be avoided in patients with asymptomatic enteric duplication cysts diagnosed by endoscopic ultrasonography.