Objective: The present study aimed at quantifying mal-positioning during thoracic endovascular aortic repair and analysing the extent to which anatomical factors influence the exact stent graft positioning. Methods: A retrospective review was conducted of patients treated between 2007 and 2014 with a stent graft for whom proximal landing zones (LZ) could be precisely located by anatomical fixed landmarks, that is LZ 1, 2, or 3. The study included 66 patients (54 men; mean age 51 years, range 17-83 years) treated for traumatic aortic rupture (n=27), type B aortic dissection (n=21), thoracic aortic aneurysm (n=8), penetrating aortic ulcer (n=5), intramural hematoma (n ¼ 1), and floating aortic thrombus (n=4). Pharmacologic hemodynamic control was systematically obtained during stent graft deployment. Pre- and post-operative computed tomographic angiography was reviewed to quantify the distance between planned and achieved LZ and to analyze different anatomical factors: iliac diameter, calcification degree, aortic angulation at the proximal deployment zone, and tortuosity index (TI). Results: Primary endoleak was noted in seven cases (10%): five type I (7%) and two type II (3%). Over a mean 35 month follow up (range 3-95 months), secondary endoleak was detected in two patients (3%), both type I, and stent graft migration was seen in three patients. Mal-positioning varied from 2 to 15 mm. A cutoff value of 11 mm was identified as an adverse event risk. Univariate analysis showed that TI and LZ were significantly associated with mal-positioning (p=.01, p=.04 respectively), and that aortic angulation tends to reach significance (p=.08). No influence of deployment mechanism (p=.50) or stent graft generation (p=.71) or access-related factors was observed. Multivariate analysis identified TI as the unique independent risk factor of mal-positioning (OR 241, 95% CI 1-6,149, p=.05). A TI >1.68 was optimal for inaccurate deployment prediction. Conclusion: TI calculation can be useful to anticipate difficulties during stent graft deployment and to reduce mal-positioning.