Duplicate address book entries

One reason you may have duplicates is that you have each contact listed under your 'iCloud' account AND under your 'on my mac' account. Only contacts in the iCloud account will sync.

Click on the ribbon in the Address Book to reveal 'Users & Groups', and then by selecting each account on the left side you will see which contacts are in which account. (make sure nothing is typed in the search field)

If this is the reason you have duplicates you have two options of dealing with the situation. Either you can leave the duplicates alone and click on one account or the other before clicking on the ribbon again to limit what you see to that account when you return to the main part of your Address Book.

Or you can delete all the contacts from one account (usually the 'on my mac' account if you want to continue syncing with iCloud). Click on the account you want to delete contacts from on the left side of the Address Book and select the first contact in the list on the right, shift click the last contact to select all and delete.

Finally, You may want to check your default account is set correctly in the Address Book preferences.

OR

Go to users and groups and choose only your On My Mac Contacts to display.

• Ensure that nothing is typed in the search field.
• Click to select the first contact and shift-click the last to select them all.
• Drag the list of contacts to your desktop.
• Delete the contacts from Address Book (using your delete key).
• Make sure your iCloud account is your default account (preferences > general).
• Select All iCloud contacts from users and groups.
• Drag the file you previously dragged to your desktop back onto Address Book.

You might want to back up all your contacts before you begin.

• Select All contacts in users and groups
• Click to select the first contact and shift-click the last to select them all.
• Drag the list of contacts to your desktop.

You might also take a look at this User Tip, to ensure you understand the differences between the different accounts in Address Book

Check out Zacharias Beckman's responses to this discussion thread: https://discussions.apple.com/thread/3374387?answerId=17196787022#17196787022

That thread isn't even about duplicates, try to keep things on topic please.

Actually, if you had read the later posts on that thread, you would realize it is. The problem of duplicate contacts being created when things were upgraded to Lion and iCloud occured because iCloud copied all of the contacts in your Addressbook into iCloud as a separate account AND left a redundant, non-active, non-syncing copy in your On My Mac account of Addressbook. There were some helpful, clarifying posts throughout that thread that I thought might be helpful for anyone trying to understand why all of a sudden after upgrading to Lion and creating an iCloud account, they had duplicates (and iCloud was no longer syncing with Google or Yahoo as it had been with Mobile Me). It's all interconnected.

Thanks Ilearnjr, really helpful link. iCloud, what a mess!

Thanks so much for the helpful information. I have cleaned up my Address Book on my iMac (Lion) by deleteing all of my ON MY MAC address book entries. I still seem to have many duplicates on my iPhone 4s. Does it take time to sync the changes via iCloud, or is there also something I need to do to erase local address book entries on the phone itself, so that I am only using the iCloud address book on my iPhone?

You may need to connect your iphone and ensure that it is not set to sync the contacts locally. It's under the info tab. Disable the syncing of contacts as iCloud will do this for you.

Thanks, this was the solution to my problem!