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Metal Gear Solid: Integral is an expanded version released in Japan only 1999. Integral is essentially a relocalized version of Metal Gear Solid based on the English-language version. Added features includes adjustable difficulty settings, a downloadable PocketStation minigame after completing the game, different patrol routes for enemy soldiers, an unlockable first-person mode and a sneaking suit outfit for Meryl.

The game also came packaged with a bonus "VR Disc", which was released as a stand-alone game in North America titled Metal Gear Solid: VR Missions and as an expansion pack of the original game titled Metal Gear Solid: Special Missions in Europe. The "VR Disc" contained over 300 VR Training missions, including 3 missions where the player take control as the Cyborg Ninja, as well as a Photoshoot Mode where Snake takes pictures of Mei Ling and Naomi Hunter and three pre-release trailers of the original MGS.

Integral served as the basis for the PC version of MGS.