Gallstone ileus is a rare but severe complication of gallstone disease where chronic inflammation of the gallbladder has formed a fistula between the gallbladder and duodenum, through which a gallstone can pass. This gallstone can obstruct the small bowel, causing ileus. These fistulae take a long time to form and are due to long-standing necrosis of the gallbladder wall due to pressure from a gallstone. Gas inside the biliary tract on imaging is diagnostic. The stones are usually larger than 2.5 cm when they cause ileus.

Gallstone ileus requires emergency surgery. An enterotomy is made proximal to the stone, and the stone is then removed. Cholecystectomy and fistula closure should be performed at the same occasion or later.