Studies with very long-term follow-up after aortic valve replacement are rare. In this thesis, very long-term outcome (survival and prosthetic valve-related major adverse events) after aortic valve replacement with or without concomitant coronary artery bypass grafting for severe aortic stenosis and/or regurgitation was determined in a cohort of 673 consecutive patients with a mean age of 65.4 ± 10.7 years who had been operated upon between 1990 and 1994 at the St. Antonius Hospital in Nieuwegein, The Netherlands. Mean follow-up after aortic valve replacement was 25.1 ± 2.8 years. Besides providing new insights on the very long-term follow-up after aortic valve replacement, some draw-backs on performing very long-term follow-up studies are also discussed, particularly the relatively large number of patients lost to follow-up due to dying from aging, especially in those with already advanced age at time of inclusion. To ensure lifelong safety for patients with a prosthetic heart valve, a plea is made to perform more long-term and very long-term follow-up studies of heart valve surgery patients by expanding and creating national and international registries for the systemic recording of long-term and very long-term follow-up data of patients with prosthetic heart valves. For this goal, the medical records of all patients with a prosthetic heart valve should be kept for life.