The most common site of intestinal obstruction in gallstone ileus is:

Gallstone ileus refers to mechanical intestinal obstruction resulting from the passage of a large gallstone into the bowel lumen. The stone enters the duodenum through a cholecystoenteric fistula. The site of obstruction by the impacted Gall stones is usually the terminal end of the ileum provided that the more proximal small bowel is of normal caliber. This pa of the intestine is the narrowest pa of the intestine. Diagnosis clue to diagnosis is obtained by presence of air in the biliary tract along with signs of small intestinal obstructions on plain x-ray. Ref : Schwaz 7/e p1451