Htm vs. aspx page extensions & duplicate content

[IvieDigital]

We have a client whose site is fairly new. There isn't much in the way of SEO results so far.

In their content management system they have implemented friendly URLs and changed the extensions from aspx to htm. Now the htm pages are all indexed in Google but when I run a campaign report in SEOmoz it shows that all pages are duplicated with there being both htm and aspx pages for each page.

Should we do 301 redirects from the aspx pages to the htm pages? Or would we be safe by removing the htm pages and letting Google reindex the site with the aspx page extensions?

Does Google have any kind of preference as to what the page extensions are as long as the  URLs include keywords?

[john4math]

It sounds like the aspx pages are still being served?  If so, you should 301 redirect them to the new friendly URLs with the htm extensions.  Google doesn't care about which page extension you use.

[NebraskaChicagohh]

You really should leave the extension alone for this exact reason - when something gets borked - you will have issues. Making friendly URL's, but like John said, you don't need to alter the extension.