Choosing the optimal aortic valve prosthesis for middle-aged patients (late 40s to early 60s) with aortic stenosis presents a challenge. The available options all have substantial drawbacks that must be considered in the decision-making process. Current data indicate that there is little or no difference in survival between mechanical and bioprosthetic aortic valve replacement in middle-aged patients at 10-15 years after surgery. Patients who receive a mechanical valve replacement have an annual risk of major hemorrhagic or embolic events of 2-4% per year for life compared with about 1% per year for patients who have a bioprosthetic valve. However, bioprostheses are associated with an increasing risk of structural valve degeneration from 10 years postimplantation, and most patients will require reoperation if they survive much longer than a decade. The mortality risk associated with reoperation is similar to that of primary surgery for most patients, and does not seem to impact on the 15-year survival in this patient group. The Ross procedure, in which the aortic valve is replaced with a pulmonary autograft, can provide improved freedom from morbidity, but operative mortality is probably double that of isolated aortic valve replacement and most patients will require reoperation. Informed patient choice is the most important factor in deciding which valve to use, with biological valves increasingly favored over mechanical valves in middle-aged patients.