The commonest site of obstruction in Gall stone ileus is -

The commonest site of obstruction in Gall stone ileus is -

1.Proximal ileum
2.Distal ileum
3.Ileocecal junction
4.Transverse colon

Explanation

Although Harrison writes the most common site to be the ileocecal valve; Sabiston, Bailey & Maingot’s write ‘distal ileum’ to be the most common site. [Maingot’s and Sabiston are highly reputed books for surgery, and are definitely more reliable than Harrison as far as surgery is concerned]
Maingot writes,
“The site of obstruction is usually the terminal ileum, just proximal to the ileocecal valve. This corresponds to the segment of the intestine with the smallest diameter.”

Bailey & Love write,
“classically there is impaction about 60 cm proximal to the ileocecal valve.”

Also know

the commonest site for gall stone impaction in CBD → Ampulla of vater.