Endosonography is an imaging method whereby a high frequency ultrasound probe is inserted into a body cavity with or without under endoscopic control. Examination of the gastrointestinal tract is performed using special echo-endoscopes or trans-endoscopic mini-probes. 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. There are some limitations for optimal examination like stenoses or other factors prohibiting a precise positioning of the ultrasound transducer. The clinical importance of endo-sonographic examinations must be continuously evaluated on the basis of new technical modalities and changes in therapeutic procedures.