Endoscopic ultrasonography of the gastrointestinal tract allows a precise ultrasound study of the accessible gastrointestinal walls (oesophagus, stomach, duodenum, rectum) and, through these walls, of the adjacent organs (lymph nodes, posterior mediastinum, pancreas, extrahepatic biliary ducts and perirectal region). This method is better than computerized tomography to evaluate the local and regional extension of oesophageal and cardial carcinomas producing little or no stenosis and of gastric and rectum carcinomas and lymphomas. It is the examination of choice to detect a perianastomotic recurrence of these cancers and to evaluate submucosal tumors of the gastrointestinal tract. This method, with no morbidity, is better than computerized tomography or ultrasonography in the aetiological diagnosis of obstacles in the biliary tract and in the diagnosis and pretherapeutic assessment of pancreatic cancer or endocrine tumors.