CO<inf>2</inf> angiography has been used extensively for the endovascular treatment of aorto-iliac and femoral-popliteal-tibial pathologies, specifically in patients with chronic kidney disease or allergy to iodinated contrast medium (ICM). However, its use in urgent treatment of an acute pseudoaneurysm has never been described before. We report a case of a 39-year-old woman, allergic to iodine, with a recent kidney transplant, who presented in the emergency room with severe pain in the left iliac fossa. Angio CT-scan showed an acute pseudoaneurysm of the left common iliac artery. She was emergently treated with a stent-graft and CO<inf>2</inf> was used as main contrast medium. The intraoperative angiographies performed with carbon dioxide showed very well the rupture site and the pseudoaneurysm; the latter were more clearly visible with CO<inf>2</inf> compared with ICM. The reported case shows the efficacy of CO<inf>2</inf> as contrast medium also in urgent settings and arterial ruptures. The lower viscosity of CO<inf>2</inf> probably leads to an easier diffusion through the arterial lesion into the pseudoaneurysmal sac. Therefore, in this case the use of carbon dioxide not only guaranteed prevention of massive allergic reaction to iodine and preservation of postoperative renal function, but also resulted in higher image quality in the operating room.