Pneumobilia, or air within the biliary tree, is a poor prognostic indicator in a patient without prior biliary sphincterotomy. Differential diagnosis includes infection with gas-forming organisms, choledochoenteric fistula in the setting of gallstones or penetrating ulcer disease, malignant invasion from a primary liver or biliary tract tumor, or metastatic disease. Treatment depends on etiology and patient factors, but often requires surgical intervention. We report a patient with gastrointestinal bleeding in whom pneumobilia was incidentally noted on abdominal plain film. Computed tomography and endoscopy revealed the biliary-enteric fistula to be caused by metastatic colon adenocarcinoma invading the biliary tree.