Endosonography is an imaging method where a high frequency ultrasound probe is inserted blindly or under endoscopic control into a lumen. Examination of the gastrointestinal tract is performed using dedicated echoendoscopes or transendoscopic miniprobes. The gastrointestinal wall, mediastinum, pancreas, bile ducts, retroperitoneum, and other structures surrounding the gastrointestinal tract are target organs for endosonography. A detailed image of pathological processes can thus be obtained. The method can be used both for primary diagnosis of lesions and in follow-up of gastrointestinal diseases. It is accurate in local staging of cancer and in detecting small lesions, which cannot be seen with other imaging modalities. There are some limitations for optimal examination like stenoses or other factors prohibiting a precise position of the ultrasound transducer. The clinical importance of endosonographic examinations must be continuously evaluated on the basis of new technical modalities and changes in therapeutic procedures.