Methods, systems, and computer readable media for DIAMETER routing with portability correction are disclosed. According to one aspect, the subject matter described herein includes a method for providing number portability correction for DIAMETER signaling involving a subscriber of a communications network. The method includes receiving a DIAMETER signaling message directed to an Online Charging System (OCS) and accessing a number portability database using the called party identifier in the signaling message, to identify if the called party has a ported number. The method further includes, in response to determining the called party has a ported number, modifying the signaling message to include results from or derived from the access to the number portability database, and routing the modified message to the OCS.