Continuity mistake: When Kevin goes to the grocery, he buys Tide detergent. While walking home, the two bags break, but no Tide detergent falls out.
Continuity mistake: In the first film, it is mentioned several times that Kevin is 8 years old. However, in this film it is stated that he is 10. When his parents are in the Miami airport security office, they say that he was left alone last Christmas. That would make him 9. Both films take place the same days, from about three days before Christmas until Christmas morning, so even if Kevin is born around Christmas time this is still a mistake.
Continuity mistake: The train that transports The Haynes Sisters and Wallace and Davis from Florida to Vermont is shown as being of the Atchison, Topeka and Santa Fe Railway in one sequence, and of the Southern Pacific Railroad in another. Neither railway ran on the east coast of the U.S.
Continuity mistake: When Apollo is getting ready to fight the Russian boxer, he comes out with white boxing gloves on. Sometime during the announcement of the fighters, the camera shows Rocky and Apollo standing in Apollo's corner. Apollo is jumping up and down while pointing with an ungloved and untaped hand, He is saying "I want you". The next time they show Apollo, he has his gloves on again. (00:26:55)
Continuity mistake: In the scene where the girl jumps to her death from the balcony, it shows her hitting the car towards the right halfway onto the windshield. Then in the next shot, it shows her lying right in the middle of the roof of the car. (00:04:05)
Continuity mistake: After he climbs out of the air duct, John McClane's shirt goes from white to green. The dirt and grime from the air duct would cause discolouration only where the shirt comes in contact with the duct. However, his shirt is uniformly green including places that wouldn't make contact and it is impossible for all surfaces to make contact even in small areas. (00:23:05 - 00:56:30)
Continuity mistake: After Sarah has called at Harry's office, Harry prepares to open his office door to see her out. The camera cuts back to Sarah for a moment, then back to the camera angle on Harry as she walks to the door. In that short space of time, the sliding cupboard doors have changed their configuration, and the blinds in the upper left of the frame have partially closed. (00:18:45)
Continuity mistake: The band-aid on Jill's doll disappears and reappears several times.
Continuity mistake: In the scene where Charlie and the snowman (his dad) are getting chased by the bullies, the sled gets split in half into two sled pieces. But you can clearly see that in some parts of this scene, Charlie is riding a real snowboard, and in others he is riding the half piece of sled.
Continuity mistake: When Uncle Lewis and Aunt Bethany have just arrived and Aunt Bethany says, "Oh dear, did I break wind?" Ellen helps Aunt Bethany fully remove her coat. Seconds later, within the same scene, Ellen is still helping Bethany off with her coat. (01:02:45)
Continuity mistake: In a scene near the end of the movie, George enters the Building and Loan with a Christmas wreath on his arm. On hearing that he has a phone call from his brother Harry, he tosses the wreath on a table and picks up the phone. In the next second, the wreath is back on his arm. (01:17:35)