you could put new tile over the old if there are no existing cracks in the floor or loose grout.

Thanks for the quick response Tileguybob. If you don't mind, I have a followup question. The replacement will not be new tiles. It'll be a layer of concrete only, I'm doing a faux stone finish with it. Will concrete adhere to the surface or do I have to prime first with sonmething else. Again, thanks so much for your response

I'm not up on concrete work but I would imagine a primer should be used to help the concrete adhere. There are Self Leveling Cements that we use over tile to get the floor flat for new tile so that may be a possibility also. I am also not sure of a minimum thickness you would need for the concrete to be. If nobody else answers here try over at http://www.floorstransformed.com and repeat your question. Thee are a few cement guys who pop in from time to time and may have the correct answer for you.

I truly appreciate your reply. I'm taking your advice. Will let you know the outcome. Have a great day.