The efficacy and safety of the new oral anticoagulants (NOAC) and the benefits of extended duration thromboprophylaxis following hip and knee replacements remain uncertain. This observational study describes the relations between thromboprophylaxis policies following hip and knee replacements across England's NHS and patient outcomes between January 2008 and December 2011. From the national administrative database, we analyzed mortality, thromboembolic complications, emergency readmission, and bleeding rates for 201,418 hip and 230,282 knee replacements. There were no differences in outcomes for either LMWH or NOAC. We found no advantage in favor of any single anticoagulation policy or in changing policy. This study supports the American Academy of Orthopaedic Surgeons' recommendation that the choice and duration of thromboprophylaxis prophylaxis be decided by the treating surgeon.