To repair a database, click with the right mouse button on the database name and select the option "Repair" in the context menu. The selected database will be checked for possible errors and inconsistent data storage and they will be fixed if necessary. Furthermore, all indexes within the database will be rebuilded.
This command creates a global write lock and blocks other operations until it is finished.
This function requires additional disk space equal to the size of your current documents plus 2 gigabytes.
More detailed explanation of this functionality can be read on http://docs.mongodb.org/manual/reference/command/repairDatabase/.