Continuity mistake: When Harold is at the drive-in diner, he grabs his fries with his left hand and then pushes the window tray off of his car with his right hand. In the next shot the fries are in his right hand, there was not enough time for him to switch hands between shots.
Deliberate mistake: The 27th floor is very tiny indeed, despite the outside view showing it to be as big as any other floor. On one end is the stairway. On the opposite side is the elevator Adam's team rides up in. There are only 4 rooms total, and between two of the room doors is the elevator ridden by the security guards. Also, logistically, the security Guard's elevator cannot be there if you notice the area at ground level where Adam's team enters their elevator.
Deliberate mistake: Blaylak was extremely intoxicated when the Green team first got to the mini-golf place but he was stone cold sober just minutes later when the White team confronted them about their poor sportsmanship.
Deliberate mistake: There is a man and a woman who do the voices on the radios Leon listens to at Game Control. The man also does the voice for 530 AM at the airport, while the woman does the voice for the airport intercom, first noticeable when the White Team arrives at the airport. The woman then does the voice of the hotel operator, "Paging Mr. Player." These two are very busy indeed.
Revealing mistake: In the scene where Harold drops the controller after playing Pong on his computer in the van, the game is still being played on the screen. In addition, it should be a paddle controller not a joystick controller.
Continuity mistake: When the game officially begins, the players can be seeing moving to their vehicles. When Adam and Laura go to leave, they see Flynch still standing there. They grab him and drag him off. Then we have a scene of the white team leaving, then the green team, then the red team, at which time in the background you can see Adam, Laura and Flynch still standing there like they were before they even started to leave.
Continuity mistake: Mrs. Grimhouse, the landlady, was brought into the hotel with her hands cuffed in front of her but in the hotel room her hands are behind her back.
Continuity mistake: The football players invade and trash the Sorority party at night. This scene is followed by day scenes of all the other groups making decisions to enter the game. Then the next scene is night again at the Sorority party, where the place is still trashed and the girls are in their night clothes. Either they didn't clean up the mess for over a day, or the editing here is off.
Continuity mistake: When Lucille is begging Harold to go back for "Little Harold" and he refuses, she then takes hold of the wheel while he's driving and turns it to the right. However, the next shot shows the van turning around left.
Continuity mistake: When the Yellow team enters the elevator to head for the 27th floor, the buttons inside are shiny and stick out and there is a red button at the top. There also only appears to be two rows of buttons. However, later when Marvin examines the panel in the elevator when they are trapped, there are 4 rows of buttons, which don't stick out, and the red button isn't there. Also, despite the power outage, the button for the 27th floor is brighter than the other buttons.
Continuity mistake: Harold's footwear changes several times during the movie. He switches between brown slippers and blue flip-flops at almost every location, most noticeably between Johnny's Fat Boy (flip-flops) and retrieving the doll afterward (slippers).
Revealing mistake: At the airport, each team has its own locker according to color. However, when the view changes to inside the locker as each team member opens it and takes out the box, it is the same locker over and over again as indicated by the scratches and scuff marks on the inside of the door.