Continuity mistake: At the end, Jeanie slams the kitchen door in Mr Rooney's face. Watch the pane of glass in the door. In all previous exterior views of the door, the pane is composed of about 4 horizontal pieces of glass. It is apparently a "jalousie" window that opens like a venetian blind, so there are no mouldings between each piece of glass. However, as soon as we see the inside of the door behind Jeanie, visible through the curtain is the silhouette of a "criss-cross" moulding grid, dividing the window into 9 panes of glass.
Visible crew/equipment: Near the beginning of the movie there is a brief scene around the empty house. While the camera is in the kitchen you can see a reflection of one of the set guys moving in the fridge handle.
Visible crew/equipment: When Ferris, Sloan, and Cameron pick up the Ferrari at the parking garage you can see the camera and its reflection in the window directly behind Ferris and Cameron.
Continuity mistake: When Jeanie meets the boy at the police station, his hair changes after every cut from her to him.
Revealing mistake: In the scene where the nurse tells Sloan in the hallway about her grandmother's passing, if you look past them, you can see Jeanie standing at the very end of the hall. Evidently she is waiting for the scene that shows the camera moving in on her later in the movie.
Continuity mistake: Cameron kicks and shatters the glass light on the front of the Ferrari towards the end of the movie. A shot of the entire garage is then shown and there is no glass on the floor.
Other mistake: In the scene where Cameron is sinking in the pool you can clearly see some kind of weight belt or something around his waist, which isn't there when he is out of the pool.
Continuity mistake: When the Ferrari goes through the window and the three of them are standing there, you can see the camera tape on the floor where they are supposed to stand. Also the broken glass on the window changes a bit over the course of that scene.
Continuity mistake: When Ferris is talking with Cameron on the phone and playing on the computer, there is no Pepsi can on his desk. A second later one appears next to his hand. The can then disappears in the next shot.
Continuity mistake: When Mr. Rooney goes to Ferris's house he is wearing a long sleeved shirt and coat jacket. A shot of his arm ringing the doorbell shows a bare arm with dark hair. When they return back to a shot of Mr. Rooney, his sleeve is touching his wrist and he does not have dark hair on the back of his hand.
Visible crew/equipment: When Ferris and gang are driving into the city (Chicago), you hear a song being played and they show an aerial view of Chicago. When they do a flyby of one of the buildings, you can clearly see the helicopter and the cameraman that is doing the filming, in the reflection of the building's windows.
Visible crew/equipment: When Ferris picks up Sloan at school he puts her in the car and walks to the left of the screen. He then enters the Ferrari from the right of the screen. He obviously had to walk around the camera man to do this. You can also see a reflection moving back and forth on the driver's side door while this is unfolding. Presumably the cameraman's.
Continuity mistake: When driving home from the city there is obviously a fake backdrop to simulate a moving car. The car can be seen to change lanes but Ferris never actually turns the wheel of the car.
Continuity mistake: In the scene where Ferris' mom comes home to check on him to make sure he's really home sick, when she's walking down the hall to enter his room you can see the door knob is a gold/old looking one. When she goes to turn the knob and go into the room, they zoom in on it and it's a crystal door knob.
Continuity mistake: In the scene where Ferris is talking on the phone with the freshmen and playing his "sick sounds" on the keyboard, his legs cross and uncross several times between shots.
Continuity mistake: At the very end of the movie when Ferris' mom is tucking him into bed the blanket is showing the line at the top then folded in and back several times.
Continuity mistake: When Cameron is on the phone with Mr. Rooney pretending to be George Peterson, Ferris calls the school. Grace picks up the phone in the outer office and tells Ferris to hold. You clearly see the third button (line three) is the one he called on. Grace says that Ferris is on line two. When Mr. Rooney puts Cameron on hold and listens to Ferris, after Ferris hangs up, the camera cuts to the phone buttons on Mr. Rooney's phone showing that Ferris was just on the second button (line two).