I didn't select .ndf because it is a suggested name, not a default. A default implies that if the user makes no other selection, the system will automatically set a value. So, if I add a new data file to a database and don't specify an extension, SQL would automatically append .ndf to the file name. This is not the case. If you add a file (in SQL Server 2000) to a database and do not include an extension, SQL Server doesn't append any extension.