On page 6 of the game's manual, there's a news article about how a protest group called A.R.S.E. (American Road Safety for Everyone) is pushing to get motorcycles banned from Liberty City, and might also be responsible for getting bicycles banned from Liberty City a few years prior. This explains the absence of bicycles and motorcycles in Grand Theft Auto III.

Within the game's data is a cut vehicle named the "Tommy". Its files are still present within the mobile release. The file names suggest that it was based off of a Mini Cooper.

The Hero Garb was originally red and blue. It was based on a Mexican wrestling outfit.

An unused HUD icon for a Ruger Autoloading Rifle can be found in the data of the PlayStation 2 version of the game. It was most likely cut early in development due to the unfinished state of the icon.

The RC Goblin, a little toy copter from Vice City, was to return but was cut. It can still be spawned with trainers, but cannot be controlled.

A functional Tear Gas weapon exists in the game, but it normally goes unused. It can be acquired with trainers.

Early beta screenshots portray Salvatore Leone with a slightly different appearance from that seen in the released game.

A pre-release screenshot showed the Avenging Angels wearing red berets instead of black caps.

Data for The Hunter helicopter is present in the game's files, and can be spawned through the use of trainers. Its weapons are working.

The title of the mission Crazy '69' refers to the film Kill Bill, where the main character, played by Uma Thurman, fights a group of Yakuza gangsters known as The Crazy 88. She uses a katana, just like Toni.

After killing Paulie Sindacco in the mission "Dead Reckoning", an elegant tombstone bearing his name appears in Liberty City Cemetery, engraved with the message "VIVA LAS VENTURAS BABY". This could be a reference to the 1964 film, "Viva Las Vegas" or to the 1963 song, "Viva Las Vegas".

The Bickle'76, a modified Taxi unlocked via the Taxi Driver side-mission, is likely named after Travis Bickle, the protagonist of the 1976 film "Taxi Driver".

Toni Cipriani was likely made in homage to Tony Soprano, the main character of the American television drama The Sopranos. Aside from their names, both characters also share ongoing problems with their mothers, who also ordered hits on them.

The PSG-1 reuses a beta model of the weapon found in the files of the PS2 version of Grand Theft Auto: Vice City.

There is unused text which states "ENGLISH.gxt/TURPASS/~W~Massacre Passed!"
"Massacre" was most likely an early name for the Rampages, although it' possible they were something else.

An early preview screenshot showed Miguel wearing an outfit identical to what he wore in Grand Theft Auto III.

The name of the mission, The Guns of Leone, is likely a play on the film ''The Guns of Navarone''.

The 'Dragon' jumpsuit is clearly modeled after the iconic yellow-and-black jumpsuit worn by Hai Tien/Billy Lo (played in part by Bruce Lee) in The Game of Death.

The Underwear and Overalls do not show Toni's chest hair, despite it being visible on Goodfella and 'The King' outfit.

In the PSP version of the game, if the player continues the side mission, Car Salesman, after level 6 and reaches level 9, a snowy weather effect starts to appear and continues appearing in further levels. This is possibly there to make driving more difficult. The snow disappears if the player fails or cancels the mission, and Car Salesman cannot be played again afterwards, so you can only see this once. This weather effect does not appear in the PS2 version of the game.

In the parking lot behind the Liberty Tree building in Bedford Point, there is a hidden sign, showing a handwritten message and Rockstar Leeds' signature smiley. The PlayStation Portable version says: "Hello again!", while the PlayStation 2 version says "You just can't get enough of this alley, can you?". The sign can be found by jumping over the walls around the lot using a tall vehicle.

In most of the mission 'The Guns of Leone' Salvatore is equipped with a Micro SMG, however in the cutscene at the end he is equipped with a Shotgun.

Maria's invitation to Toni during the final cutscene of the mission, Taken For A Ride, to join her for "coffee" at her house is an apparent reference to the Hot Coffee minigame in Grand Theft Auto: San Andreas.

In early versions of the game, Toni's casual clothes were a purple shirt with a green vest.

Despite being a main antagonist in Grand Theft Auto III, Miguel is seemingly killed in the mission Contra-Banned, set three years prior to the events of Grand Theft Auto III. It can be assumed that he somehow managed to survive.

There is an unused string of text in the game's files which hints that Assassination missions were going to return from Vice City.

A Toyota Supra and Subaru Impreza WRX are listed in text files. It is unknown what their in-game names were planned to be (assuming they would be changed).

In the strategy guide, pictures of a white Leone Sentinel can be seen. This is not available in the final game.

The name of the mission, Big Rumble in Little China, is a take on the film Big Trouble in Little China.