Gallstone ileus is a rare (1%–4%) complication of gallstone disease. Gallstones entering the gastrointestinal tract by penetration may cause obstruction at any point along their course through the tract; however, they have a predilection to obstruct the smaller-caliber lumen of the small intestine (80.1%) or stomach (14.2%). The condition is seen more commonly in the elderly who often have significant co-morbidities. Gallstone ileus causing large bowel obstruction is rare. We report the case of a 95-year-old woman who presented with a history of abdominal pain without fever, nausea, vomiting, or diarrhea. Computed tomography of the abdomen and pelvis with oral contrast revealed a high-density structure within the lumen of the distal sigmoid colon, initially suspected to be a foreign body. Medical management failed and surgical intervention was not possible. Autopsy revealed peritonitis and a rupture of the sigmoid colon at the site of a cylindrical stone found impacted in an area of fibrotic narrowing with multiple diverticula. A necrotic, thick-walled gallbladder had an irregular stone in its lumen that was a fracture match with the stone in the sigmoid. Adhesions, but no discrete fistula, were identified between the gallbladder and the adjacent transverse colon. The immediate cause of death was peritonitis caused by colonic perforation by the gallstone impacted at an area of diverticular narrowing. To our knowledge, such autopsy findings have not been previously reported.