This article reviews the recent literature on the role of endoscopic ultrasonography (EUS) as diagnostic and therapeutic tool, defines it's place in the algorithm of diagnostic procedures and informs how to treat gastroenterologic patients evaluated by EUS. Endoscopic ultrasonography utilizes the technology of endoscopy to introduce high-frequency ultrasound probes in the upper or lower part of gastrointestinal tract to visualize gastrointestinal wall and adjacent structures. Longitudinal endoscopic probe is different, compared to radial probe, and advantage is use of Doppler technique. This method has came out as an important modality for the diagnosis and staging of benign and malignant lesions of the gut wall and surrounding structures of the mediastinum, abdomen and pelvis. It is also used as a diagnostic tool for the evaluation of submucosal masses of the upper gastrointestinal tract and the rectosigmoid, for locating pancreatic endocrine tumors, and for the assessment of vascular disease. The widest application of EUS is, however, in the diagnosis and staging of esophageal, gastric, rectal, and pancreaticobiliary carcinoma. EUS has been shown to change the approach to clinical management in a significant proportion of patients to a less costly, risky, or invasive strategy.