Endoscopic ultrasonography is a combination of endoscopy and ultrasonography. This method facilitates an accurate evaluation of singular layers of the gut-walls and adjacent structures. Great gain is represented by the possibility to analyze submucosal tumors, to diagnose vascular anomalies and especially the staging of both gastrointestinal malignancies and tumors in the pancreato-biliary area. The method is also suitable for the monitoring of treatment of these malignancies (chemotherapy, radiotherapy and laser therapy) as well as for an early diagnosis of tumor recurrences. The paper enumerates the possibilities, limits, some differential-diagnostic problems, complications, as well as perspectives of this modern method.