Gallstone ileus is a complication of cholelithiasis resulting from a fistula between the gallbladder and the gastrointestinal tract. If sufficiently large, a gallstone may lodge at the narrowest part of the gastrointestinal tract, usually the terminal ileum, and present with small bowel obstruction. Here the authors present the unusual case of an 82-year-old man who developed symptoms and signs of large bowel obstruction due to an untreated gallstone, measuring 7×4.5 cm, that fistulated into the transvere colon and subsequently impacted in the sigmoid colon. An emergency laparotomy with sigmoid colotomy was undertaken to remove the obstructing gallstone, and the patient made a full recovery.