Development of the curved linear (convex) array echoendoscope has enabled procedures that utilize interventional endoscopic ultrasonography (EUS), such as EUS-guided drainage. EUS-guided pseudocyst drainage creates a fistula between the pseudocyst and the gastric or duodenal lumen. This treatment is superior to conventional endoscopic transmural drainage with respect to prevention from complications such as bleeding, because ultrasonographic observation permits easy visualization of the interposing vessels and real-time visualization of needle procedure. Endoscopic ultrasonography-guided drainage can also be applied to pancreatobiliary drainage. In cases where endoscopic retrograde cholangiopancreatography (ERCP) is unsuccessful in the treatment of obstructive jaundice and chronic obstructive pancreatitis, transmural drainage of bile and pancreatic juice under EUS guidance may supplant the percutaneous transhepatic biliary drainage and the surgical treatment.