How to rethrow the same exception in SQL Server

SQL 2012 introduces the throw statement:

http://msdn.microsoft.com/en-us/library/ee677615.aspx

If the THROW statement is specified without parameters, it must appear
inside a CATCH block. This causes the caught exception to be raised.

BEGIN TRY
    BEGIN TRANSACTION
    ...
    COMMIT TRANSACTION
END TRY
BEGIN CATCH
    ROLLBACK TRANSACTION;
    THROW
END CATCH