We present a case of iatrogenic extensive air embolism in the peripheral pulmonary arterial tree following intravenous contrast injection for a CT pulmonary angiogram performed to investigate chest pain in a 25-year-old female patient. Small volumes of iatrogenic air embolism following contrast injection are not infrequently encountered incidentally in the central vasculature (brachiocephalic veins, superior vena cava, right cardiac chambers and main pulmonary arteries). To our knowledge, however, this is the only case of extensive peripheral pulmonary arterial air embolism on CT that has been reported in the literature. Despite the extent of peripheral air, this potentially clinically significant complication was relatively inconspicuous at CT interpretation. A new radiological sign, the "double bronchus sign", is proposed as a useful diagnostic tool. In addition to discussing the imaging features, important safety considerations and principles of immediate management, relevant to all radiologists, are addressed.