Younger adults requiring aortic valve replacement often receive a mechanical valve given concerns over durability of bioprosthetic valves. However, prior studies have been underpowered to compare long-term survival implications of mechanical versus bioprosthetic valve replacement in younger adults. In this retrospective cohort from the New York Statewide Planning and Research Cooperative System (SPARCS) , 4253 patients age 50-69 receiving surgical aortic valve replacement (AVR) were studied to determine the relationship between valve type (bioprosthetic vs mechanical) and all-cause mortality. From this cohort, 1001 pairs of patient were matched on propensity scores for bioprosthetic valve replacement as determined from nonparsimonious hierarchical regression modeling accounting for clustering of patients within surgeons. In addition to assessing for adequacy of matching on propensity scores using statistical methods, 30-day complication rates were similar in the matched groups consistent with balanced operative risk. During the study period, the proportion of patients who underwent bioprosthetic AVR increased from 15% in 1997 to 74% in 2012. Over a median follow-up of 10 years, there was no difference in overall survival (p=0.74) with 15-year actuarial survival 60.6% (95% CI, 56.3%-64.9%) in the bioprosthetic group compared to 62.1% (95% CI, 58.2%-66.0%) in the mechanical prosthesis group (HR=0.97; 95% CI 0.83-1.14). For secondary endpoints there was no significant different risk for stroke (ischemic or hemorrhagic) (P=0.84), the mechanical group demonstrated a higher risk of major bleeding with cumulative incidence at 15 years of 13.0% (95% CI, 9.9%-16.1%) in mechanical group compared with 6.6% (95% CI, 48% vs 8.4%) in bioprosthetic group. The bioprosthetic group had a higher risk of reoperation with cumulative incidence of 12.1% (95%CI, 8.8%-15.4%) vs 6.9% (95% CI, 4.2%-9.6%) in the mechanical group. These findings persisted when extended to comparisons among the entire cohort.<\/p>\n