A patient with an esophageal duplication cyst who presented with dysphagia is described here. The diagnosis was accurately made preoperatively by endosonography due to the demonstration of contiguity of the muscularis propria of the esophagus with the muscle layer of the cyst wall. Endoscopic ultrasound is the most reliable nonsurgical method for the diagnosis of this lesion, assisting in surgical planning in symptomatic patients and observation in asymptomatic ones.