The following is a list of secrets, Easter Eggs, and hidden trivia references in Grand Theft Auto IV.
- GTA would not be GTA without the sex references:
- in the Memory Lanes bowling alleys, there is a neon sign displaying a bowling pin and two bowling balls, one on either side of the bowling pin; this is supposedly a subliminal reference to the male sex organs
- in many spots around Liberty City, there is rubble on the ground; in some of this rubble, you can see a purple dildo sticking out
- there are signs scattered throughout Liberty City that say 'Hot Coffee Shop,' clearly a reference to the Hot Coffee sexual content and controversy from GTA: San Andreas
- When you go down the stairs of your first apartment in Hove Beach, you may spot some graffiti referring to past GTA protagonists - Claude, Tommy, Carl, and Toni.
- You may remember Sprunk from GTA: Vice City, GTA: San Andreas, and Manhunt. It has returned to GTA IV with a brand new look. There is an entire Sprunk manufacturing plant in Alderney.
- If you ever have the time, visit the Statue of Happiness (Statue of Liberty) on Happiness Island; inside, you will be able to spot a giant beating heart. This is supposedly the "heart of Liberty City."
- In Cluckin' Bell restaurants, near the back of the store, there's an action figure of a man in a martial arts position wearing a chicken hat; printed on the glass is "Cluck Norris," which is a parody of television star Chuck Norris, an expert in martial arts and the inventor of his own martial art and the roundhouse kick.
- If you ever have time to watch the in-game TV shows in one of your apartments, you may see a TV program on one of the channels called 'Las Venturas Poker.' You will actually see a casino from GTA: San Andreas.
- One of Rockstar's rivals, THQ's Saints Row, has been parodied in the world of Liberty City on various billboards and signs throughout the city as a seafood restaurant called 'Squid Row - Budget Seafood.'
- You may remember Love Fist from GTA: Vice City. As in GTA: San Andreas, there is a reference to them on a sign in Star Junction.
- Many street names in Bohan are named after prisons.
- Leavenworth Ave
- Alcatraz Ave
- Sing Sing Ave
- Guantanamo Ave
- Attica Ave
- San Quentin Ave
- Folsom Way (best known from "Folsom Prison Blues" by Johnny Cash)
- Rykers Ave (from the fictional Rykers Island prison in Marvel Comics)
- Joliet Street
- Streets running east-to-west (horizontally) in Algonquin are named alphabetically after different types of minerals. "A" is at the southern end of Algonquin; "X" (the last letter used for a street name) is at the northern end.
- Amethyst
- Barium
- Calcium
- Diamond
- Emerald
- Feldspar
- Garnet
- Hematite
- Iron
- Jade
- Kunzite
- Lorimar
- Manganese
- Nickel
- Obsidian
- Pyrite
- Quartz
- Ruby
- Silicon
- Topaz
- Uranium
- Vauxite
- Wardite
- Xenotime
- Once you get your apartment in Bohan, look on the ground next to the coffee table in front of the bed. There are a few CDs laying on the floor. Zoom in with a sniper, and of course, one of the CDs is by OG Loc from GTA: San Andreas.
- There is a laundromat in Alderney called "Mr. Wong's," the same one from GTA III.
- If you go into any of the TW@ cafes and look at the printer, you will see an error 'ERROR UNLEASH NINJA GURU'.
- The popular television show CSI has its own parody in GTA IV, called "Science of Crime." You can find posters for this all around Liberty City.
- If you look on the walls in the prisons, you will find prison guard names, which are funny.
- Seymour Fani
- Isaac Hunt
- Richard Head
- Phil McRevis
- The mission Weekend at Florian's is a reference to the comedy movie 'Weekend at Bernie's' (Florian insists that his new name is Bernie).
- The mission called I Need Your Clothes, Your Boots, and Your Motorcycle is a reference to Terminator 2: Judgment Day, in which Arnold Schwarzenegger says this famous line.
- In the amusement park in Broker there are blue/purple Hippo Statues, just like the ones from Manhunt.
- At the Statue of Happiness, near one of the doors, there is a t-shirt that reads "Happiness Is..." on the front and "Land" on the back, as if to say "Happiness Island." You can also purchase and wear this shirt.
- When you kill Playboy X, go to his apartment to get clothes that unbelievably resemble Claude's clothes; he was the protagonist of GTA III.
- Rockstar Games has a habit of putting its logo in its games, so if you go to a bowling alley and look at the bowling pins you will see that they have the Rockstar logo on them.
- If you look at any newspaper in the game you will see a familiar face on the front, it none other than Donald Love, who if you remember, disappeared in GTA III.
- if you look at the golf courses carefully from a height you may notice that they are penis shaped.
- The securicars in GTA III had the words Gruppe Secks on, the ones in GTA IV have a similar one saying Gruppe 6.
- This is a parody of 24, a popular TV show in America on the TV Channel FOX starring Kiefer Sutherland. Also the clock that is used to say the numbers "72" is reference to the ABC show Lost.
- When you enter any of the bars in Liberty City you will see postcards of Vice City.
- There's a brand of beer in the game called 'Dusche Gold.' "Dusche" is German for "shower", so it translates into "Golden Shower."
- Burger Shot is another restaurant returning in GTA IV; this is a parody of Burger King.
- In Trailer 2, you can see two artworks from previous GTAs on the side of a building or wall. El Burro from GTA III and the motorbike from Vice City.
- When going in the Algonquin Bridge from Algonquin to Broker, you can see to the right side a Building with the Name "CLOCKTOWER" this is the resemble of the "WATCHTOWER" Building of Society of the Jehovah's Witnesses.