Conventional endoscopy can assess the location, mucosal appearance, and consistency of a gastrointestinal submucosal tumor but cannot provide enough information to differentiate the tumor from extraluminal compression by an external structure or from a neoplastic lesion or to determine whether the tumor is malignant. Therefore, endoscopic ultrasonography (EUS) has emerged as the most reliable method for evaluating submucosal tumors. EUS is very accurate in determining whether a submucosal "bump" is the result of extrinsic compression and can clearly distinguish solid from cystic structure within the submucosa, differentiate the layers of the gut wall, and define the layer of origin of the tumor. Moreover, EUS is the best way to decide whether a lesion can be resected safely and provides an indication as to whether endoscopic or surgical resection should be performed. Although various advanced EUS methods have been introduced, they require more study to determine their role in the diagnosis and staging of gastrointestinal tumors.