BACKGROUND: Patients undergoing transcatheter aortic valve implantation (TAVI) for bicuspid aortic stenosis (AS) frequently present with ascending aortic (AAo) dilatation which is left untreated. The objective of this study was to study the natural progression and underlying mechanisms of AAo dilatation after TAVI for bicuspid AS. METHODS: Patients with a native bicuspid AS and a baseline AAo maximum diameter > 40 mm treated by TAVI and in whom post-TAVI computed tomography (CT) scans beyond 1 year were available were included. AAo dilatation was deemed to be either continuous (≥ 2 mm increase) or stable (< 2 mm increase or decrease). Uni- and multivariate logistic regression analysis was utilized in order to identify factors associated with continuous AAo dilatation post-TAVI. RESULTS: A total of 61 patients with a mean AAo maximum diameter of 45.6 ± 3.9 mm at baseline were evaluated. At a median follow-up of 2.9 years, AAo dimensions remained stable in 85% of patients. Continuous AAo dilatation was observed in 15% of patients at a rate of 1.4 mm/year. Factors associated with continuous AAo dilatation were raphe length/annulus mean diameter ratio (OR 4.09, 95% CI [1.40-16.7], p = 0.022), TAV eccentricity at the leaflet outflow level (OR 2.11, 95%CI [1.12-4.53], p = 0.031) and maximum transprosthetic gradient (OR 1.30, 95%CI [0.99-1.73], p = 0.058). CONCLUSIONS: Ascending aortic dilatation in patients undergoing TAVI for bicuspid AS remains stable in the majority of patients. Factors influencing TAV stent frame geometry and function were identified to be associated with continuous AAo dilatation after TAVI; this should be confirmed in future larger cohort studies.