Check that your document is using the same page size as the paper you're printing on and that you don't have Word's option to scale the print checked (see under File|Options|Advanced>Print). Check that you're using the correct printer drivers and printer setup, too.

Do note that if you've changed printer drivers (e.g. because you've changed printers or Windows versions), that may also be a factor, as Word relies on information from the active printer driver for the page layout.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]