Continuity mistake: When Marv has just climbed out of the basement through a hole in the floor, we see him dangling facing forwards, but the shot of his legs below gives the impression he's facing sideways. He has no time to switch positions between both shots.
Continuity mistake: When the McCallisters are at the police station, the cop puts downs the phone and tells them there is "No sign of him." Behind them, the coffee pot is half full and a lady in a multi-coloured top talks with another cop. In the next shot of the McCallisters, the coffee pot is almost empty, a coffee tin with a red lid appears (that was taken away in an earlier shot) and a completely different lady talks to the cop behind them.
Continuity mistake: At the end, Harry walks to the building's door, thinking he can get in. The bag with tools opens and tools fall all over him. After a few scenes, he gets up and you can see that the tools are in one place and not scattered anymore. Plus the bag and string have disappeared.
Continuity mistake: When Kevin is checking into the hotel you can see a pair of legs in the top right hand side of the screen. At one point they walk away and then are back in the very next shot to continue standing while Kevin talks to the hotel lady.
Continuity mistake: When Harry is going to the back of the relatives' brownstone the row of houses is on the right as he walks away from the one Kevin is in. When he gets to the back the houses should all still be on his right, but the one he breaks into is on the left.
Continuity mistake: When Harry goes up the steps leading to the back door of Kevin's uncle's house, the wooden planks he kicks away are in a different position to when he first enters the alley.
Continuity mistake: Kevin asks the limousine driver, "Do you know any good toy stores?" His glass of Coke is almost empty. When the driver says, "Yes sir.", it is three-quarters full.
Continuity mistake: When the vans from the airport arrive, notice the second van to arrive smashes the statue in front of the McCallister's door all over the pavement. When the whole family is running out of the house into the vans, the statue is standing perfectly again like it hadn't been touched at all, but pieces of the feet were broken off, so it couldn't have just been stood up again.
Continuity mistake: When Kevin is running from Harry and Marv he breaks a fake pearl necklace to spread the beads all over. You can see after he drops them all that they have spread far apart. In the next shot where Harry and Marv's feet are shown there are a lot more beads all together which is why they slipped on them.
Continuity mistake: The hotel staff and security come up to Kevin's room - Kevin starts playing the tape and fast forwarding and muting when the woman in the scene talks. At the end of the scene when the man in the movie says "maybe I'm off my hinges but I forgive you" the woman lets out a sigh of relief. Kevin leaves as he plays this scene, and the sigh in the movie couldn't be heard.
Continuity mistake: Kevin's mom goes to the 3rd floor to lecture Kevin. When Kevin stands they move shots between mom and Kevin who is standing still. There are 3 separate shots of Kevin in this sequence. In the 1st & 3rd shot his left collar button is covered and his hair bang is above left eyebrow. In the second shot the left collar button is visible & the hair bang is lower touching the left eyebrow.
Continuity mistake: Kevin is carrying his dad's bag. In the shots of him running the bag is missing, he only has his backpack, but you can see it in other shots, when the guy at the hotel is carrying his bags his dad's bag is missing.
Continuity mistake: When you see Marv first step onto the green slime in the basement, he's only a few feet away from the shelf with all the paint cans. But, after he falls, he slides for a much longer time than he would need to get to the shelf from where he fell.
Continuity mistake: Before Harry jumps for the ladder, there are several close-ups and there is nothing on the bottom rung. When Harry jumps, the bottom rung is suddenly covered in green goo causing him to slip.
Continuity mistake: When Harry slips off the ladder outside, he falls backward towards the pallet on the ground (a few feet away from the ladder), but then suddenly the green slime falls from the ladder straight down onto his face. The slime would have landed on his feet or maybe legs, but by this time his face was well clear of the ladder.
Continuity mistake: Kevin takes photos of the Wet Bandits robbing Duncan's Toy Chest. Later on when the police look at a photo, it doesn't match up to when it was taken - they didn't have money in their hands.