OBJECTIVES: To compare early mortality after aortic valve replacement (AVR) between the recipients of mechanical and bioprosthetic aortic valves. METHODS: A retrospective analysis of patients 65 years or older in the 2006-2011 Medicare databases who underwent AVR. In the mixed effects models adjusting for physician and hospital random effects, we estimated odds ratios (OR) of early mortality, comparing mechanical versus bioprosthetic valves. Early mortality was measured as death on the surgery date, death within 1-30 and 31-365 days after the surgery date, death within 30 days after the hospital discharge date and operative mortality (death within 30 days following surgery, or at discharge, whichever is longer). RESULTS: Of the 66,453 Medicare beneficiaries included in the study, 19,190 (28.88%) received a mechanical valve and 47,263 (71.12%) received a bioprosthetic valve. The risk of death on the surgery date was 60% higher for mechanical valves than for bioprosthetic valves (OR, 1.61; 95% CI, 1.27-2.04; P<0.0001). The risk difference decreased to 16% during 30 days after the surgery date (OR, 1.18; 95% CI, 1.09-1.28; P<0.0001). There were no differences within 31 to 365 days after the surgery date and within the 30 days post-discharge. Risk of operative mortality was 19% higher for mechanical valves than for bioprosthetic valves (OR, 1.21; 95% CI, 1.13-1.30; P<0.0001). The number needed to treat with mechanical valves to observe one additional death on the surgery date was 290. Consistent findings were observed in subgroup analyses of patients who underwent concurrent AVR and Coronary Artery Bypass Graft (CABG), but not in isolated AVR subgroup. CONCLUSIONS: In this cohort analysis of Medicare beneficiaries, mechanical aortic valves were associated with a higher risk of death on the surgery date and within the 30 days following surgery when compared with bioprosthetic aortic valves among patients who underwent concurrent AVR and CABG, but not isolated AVR.