Gallstone ileus is a condition in which intestinal obstruction is caused by a gallstone that has traveled from the gallbladder to the gut through a fistula. Although the most common site of fistulization is the duodenum, fistulas to the colon have also been reported. In this case, a fistula developed between the gallbladder and adjacent transverse colon. Obstruction occurred at the rectosigmoid colon, a point of relative narrowing.