The game contains an unused perk called "Expose Enemy". It's code name is "specialty_exposeenemy".

The German version removed the dramatic gore effect upon Spoiler:shooting Zakhaev's hand off in the "One Shot, One Kill" mission and Arcade Mode is disabled and cannot be unlocked.

The Wii version has several differences from the Playstation 3, PC, and Xbox 360 versions:

• The ragtime warfare cheat was replaced with a paintball cheat.
• When using the "A Bad Year" cheat, you must get headshots for enemy corpses to turn into tires.
• There is no voice chat, and hence no Eavesdrop perk.
• Exclusive Squadmate mode was added for Campaign.
• Some weapons have different reload sounds.
• The Variety Map Pack is not available.

The Nintendo DS version of Modern Warfare began development as a remake of Geist for the GameCube titled Geist DS. Evidence of this can be found in the game's code.

In various missions, increasing the brightness through the use of console commands reveals that the texture for water is actually a bunch of numbers and what appears to be Arabic writing.

In the campaign mission, "The Bog", it is possible to obtain an M21 with a unique camo using console commands. It is most likely an early version of the Desert camo.

At the Beginning of the mission "The Coup" are two Arabic banners. The black one on the left translates into "Infinity Ward".

There is a reference to the movie "The Matrix" at the end of the mission Spoiler:"crew expendable", if you fail to jump from the sinking boat to the plane, you'll get the message: "Nobody makes the first jump..."

There were originally plans for a Russian Loyalist mission, as seen in some trailers. One of these possible missions involved escorting a tank.

The P90 has an unused Olive finish.

There is a cut weapon found in the game files called the Brick Blaster which is visually a USP .45 but instead fires cinder blocks and has no ammo counter.

In the "Mile High Club" level, during the opening sequence when a hole is being cut to drop into the plane, somebody says, "Surely you can't be serious". Captain Price then says, "I'm serious, and don't call me Shirley". This is a line from the movie Airplane.

There's some unused dialog for Captain MacMillan on the game's disc that is never played in-game.