Noobiiee said:Are you on a custom rom?
Some customs roms don't have maps included and you will need to redownload it from the market.
If it wont download try the follow the steps here
1. open the Root Explorer app
2. navigate to /system/apps and make the folder Read/Write
3. long press on maps.apk to rename the maps.apk to maps.apk.bak
4. make the folder Read/Only
5. reboot
6. menukey > Settings/Applications/Managed Applications/ menukey > filter > all
7. locate com.android.google.apps.maps which has a size of 0.00b
8. click it and uninstall
9. go to the market, search for google maps and install