That's not accurate. In fact, in the .NET 2.0 timeframe the opposite was the case (the 64-bit JIT would fail to honor the IL tail. prefix in many cases, though

That's not accurate. In fact, in the .NET 2.0 timeframe the opposite was the case (the 64-bit JIT would fail to honor the IL tail. prefix in many cases, though it would also make tail calls in other cases even when the prefix wasn't applied)[1]. But as of .NET 4.0, both platforms honor the tail. prefix except in a very limited set of circumstances[2] (e.g. calls from untrusted code to trusted code). As far as I know, F# is the only reasonably popular .NET language to emit the tail. prefix, though[3]. [1] http://blogs.msdn.com/b/davbr/archive/2007/06/20/tail-call-jit-conditions.aspx http://blogs.msdn.com/b/davbr/archive/2007/06/20/tail-call-j... [2] http://blogs.msdn.com/b/clrcodegeneration/archive/2009/05/11/tail-call-improvements-in-net-framework-4.aspx http://blogs.msdn.com/b/clrcodegeneration/archive/2009/05/11... [3] http://blogs.msdn.com/b/fsharpteam/archive/2011/07/08/tail-calls-in-fsharp.aspx http://blogs.msdn.com/b/fsharpteam/archive/2011/07/08/tail-c...