This study evaluated long-term outcomes of bioprosthetic and mechanical aortic valve replacement (AVR) using data from the Society of Thoracic Surgeons Adult Cardiac Surgery Database (STS-ACSD). It focused on patients who underwent primary isolated AVR, excluding those with certain conditions such as endocarditis, emergency/salvage status, or prior cardiac surgeries. The study found that, after adjusting risks, mechanical valves were associated with lower all-cause mortality compared to bioprosthetic valves for patients aged 60 or younger. These findings provide valuable information for decision-making in choosing between bioprosthetic and mechanical valves, particularly in younger patients.