Aortoenteric fistula is a rare condition that may cause death in patients due to gastrointestinal bleeding. The duodenum is the most frequently involved site, at 78.5% of 191 cases by Nagy and Marshall's meta-analysis. It is characterized by the clinical triad of abdominal pain, gastrointestinal bleeding, and an abdominal mass. Abdominal computed tomography is the most useful tool in detecting an aortoenteric fistula. To prevent a high mortality rate, early diagnosis is necessary. Exploratory laparotomy is required for patients who are highly suspected of having an aortoduodenal fistula. Herein, we report a 60-year-old man who suffered from acute gastrointestinal bleeding, recurrent syncope, and impending shock. Abdominal computed tomography revealed a 6 cm longitudinal aneurysm in the infrarenal aorta. Emergency laparotomy was performed and revealed an aortoduodenal fistula in the fourth portion of the duodenum causing acute duodenal bleeding. The patient survived and has undergone 2 years worth of regular follow-up in our outpatient department.