Continuity mistake: In the exterior front shots of Elliott's house there are some significant changes to the landscape in different shots. For instance, the two lampposts at the bottom of the driveway change to an entirely different style in some shots, and the huge garden boulders repeatedly vanish and reappear. Also, note when Michael takes off on Elliott's bike to go search for ET, the in-ground lamppost that should be beside the mailbox has vanished, but it reappears when all the government agents are setting things up outside the house.
Continuity mistake: When they are all outside and MacReady has separated the three most likely suspects and orders that they be tied down and tested, he comments at that time that they are to be hit by a storm in six hours. Cut to the scene where Mac is dictating into his recorder and he comments that the storm has been hitting them hard for 48 hours. However it is the same night and at best, maybe only an hour has passed.
Continuity mistake: As Gant is pulling the Firefox out of the hangar, it is still very dark, as in pre-dawn. But as the Russian officers are shown shooting and watching the Firefox take off, it is suddenly much lighter outside as if it is after dawn and the sun can even be seen. But it would have taken 30-60 minutes for the light level to change that much.
Continuity mistake: When little Buddy and his family are being murdered by the use of Little Buddy's Pumpkin mask, the Silver Shamrock tag on the back of the mask disappears and reappears several times.
Continuity mistake: The sequence in which Dragon is chasing Mrs. Brisby through the field, up the tree and eventually into the mill's lake, watch his eyes. The original placement is (from viewer's perspective) blue on the right and gold on the left. When he chases her up the tree the gold one is visible on the right, it then switches back when the camera cuts back to a wide shot. This happens again a few seconds later near the lake.
Continuity mistake: Tron sends his memory disk to talk to Alan. After Tron communicates with his user Alan1, Alan sends him back the disk with new data on it to destroy the MCP. When Tron receives the disk it is like a Frisbee, solid on the top and hollow on the bottom. When he receives the disk the hollow part is on the bottom. He holds the disk in front of him and starts talking about "the key to the new order". The shot changes and the disk has been reversed, hollow side toward him and solid side away from him. He did not have time to rotate the disk. (01:08:10)
Continuity mistake: When Trash shoots the bounty hunter with the grappling hook, he shoots it at his stomach. After he ties it to the bike and drives off dragging the bounty hunter, the hook is now in his back.