On the teaser site for Capital Auto Sales, it shows many cars that had different names than their in-game equivalent. These are presumably beta names for the respective cars.

The game's graphics were originally more "cartoonish".

The Butler is a cut character. The purpose of the character is unknown, however it's logical that he was intended to be Salvatore Leone's butler. The only remains are the butler's fully textured model in both gta3.img and txd.img.

The German version was heavily censored to meet a USK 16 rating. The edits made were the removal of blood, headshots and amputations taken out (although NPCs would still appear limping if shot), unable to hit anyone whilst they're on the ground (attempting to would have you flail around over them), no money dropped from killed NPCs and all rampage missions removed.

Miguel drives a Banshee for a getaway car in the opening cutscene, which is strange as there are four people in the group and a Banshee has only two seats. This could be hinting Catalina's betrayal.

The Kuruma is referenced in an episode of CBS crime drama "NCIS" where a witness tells Ziva David that the getaway car was a "Kuruma", who gets told by her superior Agent Gibbs that "kuruma" means car, and that her description of the car is car. Agent McGee steps in and tells his confused co-workers, "Kuruma is the name of a car in Grand Theft Auto III, it's a Chrysler Sebring Sedan, boss."

King Courtney's spoken orders in the mission Gangcar Round-up incorrectly state that the Diablo gang car is an Infernus. The subtitles, however, call it a Stallion.

Mr. Wong's Launderette's sign incorrectly spells Launderette as "Laundrette".

The musician Tom Novy was set to appear in the game along with his song "Back To The Streets" but both were cut from final release. However, his model can still be found in the files.

Originally the Triads had black outfits and tattoos.

Early screenshots show that buses were originally supposed to appear in-game.

Children and elderly people with walkers were planned for the game, but were cut.

Claude could originally run with the baseball bat.

Some early copies of GTA III still featured the logo of DMA Design, the original name of Rockstar North, during the opening credits.

The beta version of GTAIII's HUD had a life bar instead of percentages.

Ads can be spotted all over the city for "Top Down City", starring Arnold Steelone (a reference to famous action film actors Arnold Schwarzenegger and Sylvester Stallone). The film is a reference to Grand Theft Auto 1 and 2, as these games are in the top-down perspective.

Officially, the protagonist's name in this game is "Claude". Hacking into the game's files, one can find a text string saying "DEFNAME = CLAUDE" which not only made it clear his name was Claude, but also hinted at a removed mechanic allowing the player to rename the main character. As a result, many also believe he is Claude Speed, the protagonist of GTA2.

Sam Houser claimed that the GTA3 protagonist did not have a name as he was merely the player's avatar, but would later be named "Claude" as of San Andreas, as everyone had taken to calling him that.

There were plans of putting a homeless man named Darkel in the game. His missions were to supposedly have you blow up buildings. He was removed after 9/11 attacks, possibly due to the developers thinking Darkel's character was in bad taste. Despite this, Darkel still remains listed in the manual credits and his character remains in the game's data.

Rockstar claimed that Darkel was removed because he did not tonally fit with the rest of the game, and his removal wasn't related to 9/11.