Spoiler:After finishing the mission Undertaker, the player finds themselves in front of the grave of the McrReary brother they killed on the previous mission, "Blood Brothers". If the player killed Derrick McReary the they can walk through his gravestone; however, the same doesn't happen with Francis's gravestone, which is solid.

The Rhino was originally going to appear in the game, but it was cut. There are still lines of code within The Lost and Damned files that show this.

There were two cut random character missions in The Ballad of Gay Tony. They both involved Luis running into ex-girlfriends. One mission has Luis taking the ex-girlfriend home and defending himself from her brothers, while the other involved the ex planting a bomb in Luis' car. It is unclear if these missions involved the same girlfriend, or two different ones.

In the 2009 edition of The Guinness Book of World Records: Gamer's Edition, Grand Theft Auto IV is credited as the "Largest Voice Cast in a Video Game" with 861 voice actors: 174 individuals voicing the main cast and voice-overs and the remaining 687 were mostly volunteers who wanted to be part of the game in some way.

There is an unused variant of the website PeepThatShit.com which refers to Outlook Park as Overlook Park.

If you stay still on the step 2 of the Higgins Helitours Heliport's ladder and the NPCs try to climb up, a glitch will happen where said NPC will be sent flying away.

Companion characters have no crash animation for when they are talking on the phone.

There's a glitch at the Windmill Street Station's southern platform. If the player hits a pedestrian and tumbles into either side of the stair barrier, said pedestrian will begin to start twitching and contorting violently.

The Australian console versions of the game originally censored many features, including shortening prostitute pickups and removing the animations, as well as removing any blood from shooting NPCs, or the player being damaged. These changes were reversed after the PC version was released.

There are unused strings of text in The Lost And Damned referencing a cut mission for Stubbs. In the mission, Johnny had to blow up a truck with a bike armed with a bomb that would arm itself at 88mph, but would explode if your speed dropped below 88mph.

The mission may be a reference to the movie "Speed", which features a bus armed with a bomb that detonates if dropping to a certain speed. A mission with a similar concept was present in Grand Theft Auto: Vice City.

An update released three days before the game's 10th anniversary on April 26th, 2018 added new songs to radio stations, while simultaneously removing songs due to licensing-expiration issues. Among the many song replacements, the Electro-Choc, Fusion, JNR, Massive B, and Tuff Gong radio stations remained untouched, while almost every song featured in the Vladivostok FM station was cut and replaced with new songs with one exception, "Liberty City: The Invasion" by Seryoga, an original song written for the game's soundtrack. These changes also carried over to the Episodes from Liberty City DLC expansions.

There are animations, a model and texture related to an unused wooden plank weapon that NPCs would have carried, specifically by the dockworkers at East Hook. An NPC can be seen holding this plank in the first trailer for the game.

In The Ballad of Gay Tony DLC mission, "Caught With Your Pants Down", Luis was originally supposed to meet Yusuf in Westminster to pick up his Buckingham Swift helicopter. In the final game, Luis meets Yusuf at Star Junction, and he already has the helicopter.