If you keep your URL's the same the effects tend to be insignificant to modestly negative at worst. They can even be positive if structural issues are improved upon. The more changes you make though the more likely it is that an issue may arise. For example, change the design and sitewide page titles and you may see more of a blip. Change the design, the page titles and stir in some 301's, worse still. Etc.

At least, that generally sums up what I've seen across a universe of quite a few site overhauls.

>> They can even be positive if structural issues are improved upon.

caveat - you will likely see a short-term dip in your rankings as the engines re-index your site. Don't worry. If your work is solid then you will see the rebound as well. If not, get in there and review what you've done for obvious errors - like redirects on any URLs that you've retired.

Dunno lorax. I understand the OP to be talking only about a redesign...not URI changes. If so, I've seen redesigns that helped volume with no dip. URI changes a different matter...but even those if limited can be more good than bad.

If it's just design changed, my experience is it depends on the before/after code.

Perhaps the OP could clarify. A "redesign" to me means a ground up rebuild - code, URIs, etc.... Visual redesign - on the other hand - would be a different matter.

Don't change your permalink structure, your urls will remain the same and changing the theme shouldn't have much impact.

One thing that could potentially affect you: if you're moving to a theme that substantially changes the internal linking structure of the site with big navigation changes or the like. (some themes come with plugins/widgets to do this type of thing - mostly beneficial results, though)

LisaB

naah, redesign only meant changing one free wordpress theme to another free wp theme :)

Then you're good to go. :)

I am just wondering does using a free theme makes any effect ? or to put it other way, does using a custom theme gives you some sort of slightest advantage ?