It will be spot the celebrity when Entourage opens today.
Among the actors and celebrities playing themselves in cameos are Gary Busey, Mike Tyson, Mark Wahlberg, David Spade, Tom Brady, George Takei and Ed O'Neill.
There are also some big names - like Billy Bob Thornton - who are incharacter.
The HBO TV series on which Entourage the movie is based, regularly featured stars playing themselves, just not this many at once.
The cameo has a long history in Hollywood. Alfred Hitchcock made cameo appearances in 39 of his 52 films. Jim Parsons appeared in the 2011 Muppets film and Alice Cooper made a cameo in Wayne's World, in 1992.
Here's some of our favourite movies which feature celebrities playing themselves.
Mike Tyson in a scene from the film The Hangover.
The Hangover: Boxer Mike Tyson plays himself - not for the first time. Tyson loves a good cameo. Other movies in which Tyson plays himself include Black & White, Scary Movie 5 and Rocky Balboa.
Ted: There were several uncredited cameos in the comedy film but it was the blast-from-the-past actor Sam Jones, who was once Flash Gordon, that got people's attention.
Zoolander: The cameos in Zoolander are of Entourage proportions. Among those credited with playing themselves are billionaire Donald Trump, actor Christian Slater, musician Lenny Kravitz and designer Tommy Hillfiger.
The Wedding Singer: Billy Idol played a small but important role in the Adam Sandler comedy. Idol's cameo in the film steals the show, especially since he plays a pivotal part in uniting Robbie (Sandler) and Julia (Barrymore). As an actor Billy makes an excellent singer.
Drew Barrymore and Adam Sandler star in The Wedding Singer.
Sex And The City 2: Liza Minnelli rocks the wedding of Stanford and Anthony with her performance of Beyonce's Single Ladies (Put A Ring On It) in her standard sequined black mini kaftan. The sequel also features Miley Cyrus.
Wayne's World: Alice Cooper's cameo in Wayne's World sees Wayne and Garth bow down and utter the famous line - "we're not worthy". Cooper has also appeared in Freddy's Dead: The Final Nightmare and John Carpenter's Prince of Darkness.
Borat: Pamela Anderson appears as Borat's guiding light to his tour of America. The former Baywatch star is forced to run for her life after Borat encounters her at a book signing.
