A retrospective assessment of the presence of air in the biliary tract is presented, based on plain film findings in 16 proven cases of gallstone ileus. In addition to five cases that demonstrated air in the biliary radicles, four cases exhibited air exclusively in the gallbladder and duodenal bulb. A clearly identifiable radiographic appearance composed of two adjacent small air-fluid levels in the right upper quadrant is described. This radiographic feature represents the air- and fluid-filled duodenal cap adjacent to the visualized shrunken gallbladder. Recognition of this combination of findings helps in establishing a prompt preoperative diagnosis in cases of gallstone ileus.