Abstract Objectives We aimed to determine whether body mass index (BMI) is a prognostic indicator for long-term, all-cause mortality in patients undergoing transcatheter aortic valve implantation (TAVI). Background Obesity in patients with established cardiovascular disease has previously been identified as an indicator of good prognosis, a phenomenon known as the “obesity paradox”. The prognostic significance of BMI in patients with severe aortic stenosis (AoS) undergoing TAVI is a matter of current debate, as published studies are scarce and their results conflicting. Methods This is an observational, retrospective study involving 770 patients who underwent TAVI for AoS. The cohort was divided into three groups based on their BMI: normal weight (≥ 18.5 to < 25 kg/m2 ), overweight (≥ 25 to < 30 kg/m2 ) and obese (≥ 30 kg/m2 ). The predictive effect of BMI on all-cause mortality 3 years following TAVI intervention was analysed using a Cox regression. Results 155 patients died during follow-up. The overweight group ( n = 302, 38.97%), experienced a lower mortality rate compared to the normal weight and obese groups (15.9% vs 25.7% and 21.0%, respectively log-rank p -value = 0.036). After adjustment by logistic EuroSCORE, being overweight was found to be an independent protective factor against mortality (HR: 0.63 95% CI: 0.42 to 0.94, p = 0.024). This was not the case for obesity (HR: 0.92 95% CI: 0.63 to 1.35, p = 0.664). We therefore describe for the first time, a “J-shaped” regression curve describing the relationship between BMI and mortality. Conclusions BMI is a predictive factor of all-cause mortality in AoS patients undergoing TAVI. This relationship takes the form of a “J-shaped” curve in which overweight patients are associated with the lowest mortality rate at follow-up.