Help!!! I upgraded to Mavericks and a whole bunch of mail disappeared from my gmail inbox!

I can confirm what Bob posted: open your GoogleMail or GoogleApps e-mail inbox directly in a browser and mark them all as "unread". Then sync your e-mails in Apple Mail by clicking "Send & Receive All" (or whatever it's called in the English Apple Mail user interface). Then, in your GoogleMail, mark them all as "read" and sync again.

That's it, the e-mails will show up correctly.

I had zero messages in my mac mail inbox but 33 in my gmail inbox. I marked the messages as unread in gmail and they all appeared in my mac mail. I then marked them unread.

A Mail update for Mavericks is now available.

Mail Update for Mavericks includes improvements to general stability and compatibility with Gmail, including the following:

• Fixes an issue that prevents deleting, moving, and archiving messages for users with custom Gmail settings
• Addresses an issue that may cause unread counts to be inaccurate
• Includes additional fixes that improve the compatibility and stability of Mail

Download here