Resuscitative endovascular balloon occlusion of the aorta (ReBoA) is a technique where a balloon is advanced through the common femoral artery and temporarily inflated for treatment of cardiac arrest or non-compressible haemorrhage. the aim of this study was to measure intravascular distances relevant for correct placement of the ReBoA catheter using computer tomographic (ct) scans. in a series of CT scans of the aorta from 100 patients diagnosed with severe aortic stenosis planned for transcatheter aortic valve implantation, we measured the intravascular distance from the insertion site in the common femoral artery to two potential zones for placement of the ReBoA catheter; between the left subclavian artery and the celiac trunk (Zone 1), as well as between the aortic bifurcation and the distal takeoff of the renal arteries (Zone 3). The mean (± SD) intravascular distance from the femoral artery to intra-aortic Zone 1 was 36 (± 2.5) cm for the lower border and 60 (± 4.1) cm for the upper border, respectively. For intra-aortic Zone 3, the mean (± SD) intravascular distance was 21 (± 2.1) cm to the lower border and 31 (± 2.3) cm to the upper border. Calculated potentially safe intervals for placement of the REBOA in Zone 1 was with 99.7% likelihood between 43 and 48 cm. No similar potentially safe interval could be calculated for Zone 3. According to this cohort study of patients with severe aortic stenosis, the balloon of the ReBoA catheter should travel intraarterially between 43 (lower limit) and 48 cm (upper limit) from the site of insertion into the common femoral artery, which would lead to correct placement in intra-aortic Zone 1 in 99.7% of cases. In contrast, no potential safety interval could be similarly defined for insertion in Zone 3. Until the introduction of resuscitative endovascular balloon occlusion of the aorta (REBOA), compression of the descending or abdominal aorta was done with external clamping via resuscitative thoracotomy or laparotomy during severe haemorrhage to minimize blood loss 1,2. Occlusion of the aorta minimizes the haemorrhage from arteries distal to the occlusion and simultaneously redirects the circulating blood to upper body, e.g. the coronary and cerebral vascular territories 3. Complete occlusion of the aortic lumen is possible for several minutes without complications, which may allow for surgical repair of the injury 4-6 , or for cardio-pulmonary resuscitation to achieve recovery of spontaneous circulation in the case of cardiac arrest. Depending on the type of injury, the REBOA catheter is inserted intra-arterially through the common femoral artery and a balloon is inflated when it is located between the celiac trunk and the left subclavian artery (Zone 1), or between the aortic bifurcation and the distal border of the renal arteries (Zone 3). In contrast, occlusion between the celiac trunk and the distal border of the renal artery (Zone 2) is generally not recommended (the so-called no-occlusion zone) (Fig. 1) 7. The indications for REBOA include, but are not limited to...