Endoscopic ultrasonography of the digestive tract provides for a precise ultrasonic study of the accessible gastrointestinal walls (esophagus, stomach, duodenum, rectum) and through the walls, of the adjacent organs (lymph node clusters, posterior mediastinum, pancreas, extrahepatic biliary ducts and perirectal environment). This method is more efficient than computerized tomography to evaluate the local and regional extension of esophageal, gastric and rectal carcinomas, producing little or no stenosis. It is the examination of choice to detect a perianastomotic recurrence of these cancers in the aetiological diagnosis of obstacles in the biliary tract and in the diagnosis and the pretherapeutic assessment of pancreatic cancers.