Concerns have been raised about the durability of the first-generation Mitroflow aortic bioprosthesis (model 12 A-LX) due to the lack of anticalcification treatment. This study reflects a 10-year experience with this prosthesis for aortic valve replacement. From June 2003 to May 2012, the Mitroflow prosthesis was used for aortic valve replacement in 510 patients, of whom only 467 with complete clinical follow-up were included for analysis. Study end-points were survival and incidence of structural valve degeneration (SVD). Analysis of SVD was based on cumulative incidence function and competing-risk Cox regression. The mean patient age was 76.4 ± 6.1 years. Valve sizes from 23 to 25 were used in 70.4%, whereas sizes from 19 to 21 were used in only 19.2%, thereby avoiding patient-prosthesis mismatch in 89.1%. Within a median follow-up time of 6.6 years (interquartile range 4.4), a cumulative 2375 patient-years, the survival rate was 86.2%, 67.3% and 33.3% at 1, 5 and 10 years, respectively. The cumulative incidence of SVD, with death as a competing risk, was 0%, 0.7% and 6.2% at 1, 5 and 10 years, respectively. Only age <75 years tended to affect the late hazard of SVD (hazard ratio 0.50, 95% confidence interval 0.23-1.08, P = 0.08), regardless of valve-specific issues. The data do not support the concerns about early accelerated structural degeneration of the first-generation Mitroflow bioprosthesis used for aortic valve replacement in patients older than 75 years. We postulate that limiting the number of small prostheses using a proper implantation technique has enhanced the reduction in risk of significant patient-prosthesis mismatch as the main determinant of early SVD. © The Author 2017. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved.