Continuity mistake: In the underground garage scene with Russ, Rusty and Janet, Rusty's hair is combed straight down and very neat when he comes out from behind the pillar. When Janet says, "I should have worn my magic bra and panties.", Rusty starts laughing and his hair is messed up. But then when Rusty is snapping his seat belt as he's sitting in the Porsche, his hair is back to being neat.
Continuity mistake: At the end, when Russ is driving to make up with the girl, the streets look very wet, as if it had recently rained. Yet, when he pulls into the driveway, that cement is totally dry.
Continuity mistake: When Russ and Rusty come out of the tunnel (with red airplane), Russ pulls off the road because their car, clothes, etc. have gone back to 1968. As they are pulling off onto the dirt, they stop just past a pickup truck with a motorcycle next to it. The next shot of the area show Russ sitting up on the back of the seat while the camera pans the area. The pickup truck and motorcycle have disappeared.
Continuity mistake: After the fight at school, Rusty's/Russ' dad comes home and takes his wife inside. When he comes back outside, he grabs Rusty by the front of his jacket, but in the next shot he is holding Rusty by the upper arm.
Continuity mistake: In the scene where Rusty is found eating popcorn and watching TV, Russ (the adult one) spins Rusty's chair around. Rusty throws his popcorn up on surprise, getting it everywhere. Then, all of a sudden, the popcorn is gone. But, moments later, it's back again.
Continuity mistake: In the scene when Russ is in the kitchen making a sandwich, Rusty comes in and Russ starts shaking the sandwich at him. You see bits of bread fly onto the bench in front of Rusty, but when the camera cuts back to Rusty again, the chunks of bread are gone
Continuity mistake: When Rusty's/Russ' dad pulls into the driveway of their home, we see the street is black and wet, like it had just rained. But when we see Russ watching from across the street, the pavement is dry and very light colored.
Audio problem: At the end of the movie, the jet plane takes off and flies overhead, but the sound is that of a propeller-driven plane, not a jet-engined plane.
Continuity mistake: When Bruce Willis is in the bathroom, taking powerful medicine, he takes the lid off a bottle of water, drops the pills all over the floor, picks up several on his way over to the door, sits down and takes the lid off the water again.
Continuity mistake: In the scene where the young Rusty goes home with his mom after beating up the bullies his father is yelling at him outside. There are close up shots and non-close up shots, in the close up shots his father's hands are on Rusty's shoulders but in the other shots they are on his face.
Continuity mistake: In the diner near the end of the movie, Russ and Rusty go to toast their chocolate milk shakes. It looks like Russ actually misses or barely grazes Rusty's glass and then starts to spill. But the very next shot they are holding their glasses upright.
Continuity mistake: When Amy is watching Rusty from the doorway, you can see her left ear is red. Moments later when she is talking to Russ, her ear is back to a normal colour.
Continuity mistake: After they meet their future pilot self outside the diner, as he gets on the plane, the front wheel is chocked front and rear. A few seconds later both chocks are gone and there is no-one else nearby. (01:32:00)