This study sought to determine the incidence, clinical impact, and changes over time of mitral regurgitation (MR) in patients with low-flow, low-gradient aortic stenosis (LFLG-AS) undergoing transcatheter aortic valve replacement (TAVR). Few data exist on the clinical impact and changes in severity over time of MR in patients with LFLG-AS undergoing TAVR. A total of 308 TAVR candidates with LFLG-AS were included. Patients were categorized according to MR severity at baseline, and presence of MR improvement at 12-month follow-up. Clinical outcomes were assessed at 1 and 12 months (+ echocardiography), and yearly thereafter. Baseline mild and moderate-to-severe MR were present in 118 (38.3%) and 115 (37.3%) patients, respectively. MR was of functional and mixed etiology in 77.2% and 22.7% of patients, respectively. A total of 131 patients (42.5%) died after a median follow-up of 2 (1 to 3) years. Baseline moderate-or-greater MR had no impact on mortality (hazard ratio HR: 1.34; 95% confidence interval CI: 0.72 to 2.48) or heart failure hospitalization (HR: 1.02; 95% CI: 0.49 to 2.10). At 1-year follow-up, MR improved in 44.3% of patients and remained unchanged/worsened in 55.7%. The lack of MR improvement was associated with a higher risk of all-cause and cardiac mortality (HR: 2.02; 95% CI: 1.29 to 3.17; HR: 3.03; 95% CI: 1.27 to 7.23, respectively), rehospitalization for cardiac causes (HR: 1.50; 95% CI: 1.04 to 2.15), and an increased overall-mortality/heart failure rehospitalization (HR: 1.94; 95% CI: 1.25 to 3.02). A higher baseline left ventricular end-diastolic diameter and a higher increase in left ventricular ejection fraction were found to be independent predictors of MR improvement at 1-year follow-up (odds ratio: 0.69; 95% CI: 0.51 to 0.94; and odds ratio: 0.81; 95% CI: 0.67 to 0.96, respectively). Most TAVR candidates with LFLG-AS had some degree of MR, of functional origin in most cases. MR improved in about one-half of patients, with larger left ventricular size and a higher increase in left ventricular ejection fraction post-TAVR determining MR improvement over time. The lack of MR improvement at 1 year was associated with poorer outcomes.