Background: Pulmonary hypertension is characterized by extensive remodelling of the pulmonary tree, with enlargement of the pulmonary arteries. The predictive value of pulmonary hypertension in patients undergoing transcatheter aortic valve replacement (TAVR) has been demonstrated. We aimed to evaluate the prognostic impact of the pre-procedural main pulmonary artery (mPA) enlargement, assessed by computed tomography angiography, in patients undergoing TAVR for severe aortic stenosis (AS). Methods: We retrospectively analyzed 337 consecutive patients with AS from our local registry who underwent right heart catheterization and computed tomography angiography before TAVR. The cohort was divided into 2 groups according to the presence of an enlarged mPA (mPA axial diameter ≥ 29 mm for male patients and ≥ 27 mm for female patients, mPAe, n = 192, mean age 83 ± 6 years, 41% male) or not (mPAn, n = 145, mean age 84 ± 6 years, 46% male). The primary endpoint was all-cause mortality at 1 year. Results: A significant correlation between invasive mean pulmonary artery pressure and mPA axial diameter was noted (Pearson r = 0.393, P < 0.001). Compared with the mPAn group, patients with an enlarged mPA had higher 1-year mortality rates (hazard ratio [HR]: 2.59, 95% confidence interval [CI]: 1.11-6.04, P = 0.027). The prognostic significance was even stronger after indexing the mPA diameter to the ascending aortic diameter (HR 3.83, 95% CI: 1.85-7.87, P < 0.001). This measure remained significant after adjustment for baseline comorbidities (adjusted HR 4.2; 95% CI: 2.00-8.98, P < 0.001). Conclusions: Pre-procedural mPA enlargement is strongly associated with 1-year all-cause mortality in patients undergoing TAVR. This finding may pave the way for a more precise noninvasive risk stratification in patients with severe AS.