Backup file created by The Sims 3, a life simulation game that gives you control over simulated persons, or "Sims," and how they interact with their world; contains saved game data up until the most recent save, which is contained in the .SIMS3 file; includes game progress like new vehicles, buildings, and characters; located in the "Saves" folder of the The Sims 3 directory along with the SIMS3 file.

If you have a corrupt SIMS3 file that does not load, you can restore the game from your SIMS3.BACKUP file. Copy the SIMS3 and SIMS3.BACKUP files and paste them into another folder for backup purposes just in case you make an error. Go back to your "Saves" folder and delete the SIMS3 file that is not loading and delete it. Remove the ".BACKUP" from your SIMS3.BACKUP file so that it looks exactly like the corrupt SIMS3 file you just deleted. You are now able to load your game from the game menu.