BACKGROUND : Both biological and mechanical prosthetic valves are treatment choices for aortic valve replacement. We aimed to characterize the selection of prosthetic aortic valves among elderly Medicare patients. METHODS : This was a retrospective analysis of patients aged 65 years or older who underwent aortic valve replacement alone or in combination with other procedures in the 2006-2015 Medicare databases. Patients were continuously enrolled in Medicare Part A and B. We characterized the trends and regional variation of the selection of prosthetic valves. Multivariable logistic regression was used to evaluate the determinants that influenced the selection of prosthetic valves. RESULTS : During the study period, there were 272,921 Medicare patients aged 65 years or older who underwent aortic valve replacement and met the inclusion and exclusion criteria. The selection of mechanical aortic valves decreased from 32.0% in 2006 to 24.3% in 2015 (P < .01). In comparison with 18.5% from northeastern states, 34.6% of patients from southern states selected mechanical valves (P < .01). Major determinants of the selection of prosthetic valves include age, gender, region, hospital characteristics, and physician experience. Patients being older, male, living in the northeast region, operated on in a high-volume hospital, and by more experienced physicians were more likely to receive biological valves. CONCLUSIONS : A 24.1% decrease in the selection of mechanical aortic valves was observed among elderly Medicare patients from 2006 to 2015. A dramatic regional difference was observed in the choice of prosthetic valves across the nation.