The Call of Duty: Modern Warfare 2 "Stimulus" map pack saw more than 1 million downloads in its first 24 hours of availability, according to publisher Activision.
The downloadable content was released on Xbox Live on March 30, with more than 2.5 million downloads in the first week.
Two map packs were initially announced by Activision, both of which will be 30 day exclusives for the Xbox 360 version of the game.
The map pack contains five new maps for the game, three brand new designs and two based on maps from earlier title Call Of Duty 4: Modern Warfare.
The downloadable content has proven controversial with some fans, in part due to its high cost of 1200 Microsoft Points ($15/£10.28) - more than previous Call of Duty map packs.
There was also considerable server disruption on the day of the pack's release, with some in-game features being affected. Although none of these issues appear to have affected its financial success.