A patient with traumatic thoracic injury and hypovolemic shock is presented to stress important differences in preoperative and postoperative aortic diameters. The patient had a blood pressure of 80/40 mm Hg. A diagnostic computed tomography angiography revealed a rupture of the thoracic aorta, and a thoracic endograft was sized based on these data. However, the postoperative computed tomography angiography (Riva-Rocci, 164/70 mm Hg) showed an increase in aortic diameters of about 30% at multiple levels. In this patient, with rupture of the thoracic aorta and hypovolemia, the aortic diameter was significantly decreased. This indicates that adequate preoperative sizing for endovascular repair of vascular pathology in patients in shock is complicated.