Aims: Aortic stiffness, measured as aortic pulse wave velocity (PWV), is a powerful predictor of cardiovascular health but is difficult to accurately obtain non-invasively. This study sought to develop a novel CT aortic stiffness index (CTASI) which incorporates both anatomical (calcification) and physiological (distensibility) aspects of aortic health. Methods: Invasive PWV and CT scans were obtained for 80 patients undergoing TAVI (cohort 1). CT data alone were obtained from an additional 238 patients (cohort 2). Aortic calcification was quantified using a modified Agatston’s methodology. Distensibility-PWV was calculated from minimum and maximum ascending aorta areas. Linear regression of these values was used to construct CTASI from cohort 1. CTASI was then calculated for cohort 2 who were prospectively followed-up. Results: CTASI correlated with invasive PWV (rho = 0.47, p < 0.01) with a higher correlation coefficient than distensibility-PWV (rho = 0.35, p < 0.01) and aortic calcification (rho = 0.36, p < 0.01). Compared to invasive PWV, CTASI had a good accuracy as a diagnostic test (AOC 0.72 [95% CI 0.61–0.84]), superior to aortic calcification and distensibility-PWV alone (χ = 0.82, p = 0.02). There were 61 deaths during a median follow-up of 771 days (95% CI 751.4–790.5). CTASI was able to predict 1-year mortality (OR 2.58, 95% CI 1.18–5.61, p = 0.02) and Kaplan–Meier survival (log-rank p = 0.03). Conclusion: CTASI is a stronger measure of aortic stiffness than aortic calcification or distensibility alone. Given the prolific use of CT scanning for assessing coronary and vascular disease, the additional calculation of CTASI during these scans could provide an important direct measurement of vascular health and guide pharmacological therapy. Graphic abstract: [Figure not available: see fulltext.].