Duplicate Content with rewrite?

[ukgimp]

For an existing site that uses a simple ID number to get the required page from a DB are there any issues during a changover from non rewrite to re written URL's.

For example if the current site has hundreds of individual pages in Google with the (php?id=X) what implications are there for duplicate content as both pages will still work (somedir/X/)

Do you need to create a 301 redirect to forward all these variations.

Cheers

[Birdman]

I would say yes, do the redirects.