Gallstone ileus is a bowel obstruction secondary to gallstone impaction at some point of the gastrointestinal tract due to the existence of a bilioenteric fistula. It is an uncommon cause of small bowel obstruction, accounting for only 1-4% of all intestinal obstructions. In patients with cholelithiasis, only 0.3-0.5% reportedly develops gallstone ileus. We report a patient with gallstone ileus who presented with small bowel obstruction that was initially misdiagnosed. The correct diagnosis was made based on finding an ectopicgallstone and a cholecystoduodenal fistula on computed tomography. We will discuss the contribution of the various paraclinical examinations for his diagnosis.