Continuity mistake: When Kevin is leaving the church after talking to the old man that lives next door to him, he runs home. Between leaving the church and getting home he is wearing one pair of trousers, when he gets home he is wearing a pair of jeans, then when he is setting up the traps for the bad guys he is back to other pair of trousers.
Continuity mistake: When Joe Pesci places his hand on the red hot doorknob on the front door of Kevin's house, he places his hand on the doorknob sideways, but after he sticks his hand in the snow, he looks at his hand and the letter M that was burned into his hand is straight up and down, not sideways like it should be based on how he grabbed the doorknob.
Continuity mistake: In the scene where Kevin prepares to ride his toboggan down the stairs, the front door changes position between half open and completely open.
Revealing mistake: When Harry trips on the fan string throwing feathers all over him, the fan sound is heard running but there's no air blowing at him as the feathers are falling around him undisturbed. A few shots later, we see the fan on and blowing feathers around the room which is what it should have been doing.
Factual error: When Kevin's mom leaves Paris to return home, the plane shown departing the airport is a DC-9. No airline uses this plane for trans-Atlantic service - it doesn't have the required range.
Revealing mistake: When the family is rushing all over the house because they're late, they show Brooke coming down the stairs and Heather going up the stairs. Then the scene goes to Mitch Murphy and then comes back to the family rushing. The scene shows the same shot of Brooke and Heather going down and up the stairs.
Continuity mistake: When Kevin is putting washing in and taking clothes out of the dryer, he places the orange bottle of liquid on top of the washer with the handle facing away. On taking the clothes out of the drier and closing the door, he turns to see the metal heater scaring him by saying "Kevin." Look over his left shoulder when the shot comes back to Kevin, the orange bottle now has it's handle facing outwards, and the top isn't on properly.
Revealing mistake: The morning the McCallisters are rushing to get to the airport, the kid from across the street is bothering one of the van drivers. In the scene where the van driver says, "Gee, kid I dunno, hit the road," you can clearly see the kid mouthing the words as the man speaks.
Revealing mistake: When Marv is trying to break into the basement with the crowbar but slips on the ice, he hooks the crowbar on the sill of the door and then slips again. The crowbar then falls on his head. The mistake is that when he slips and the crowbar is hanging it is not hooked on the sill of the door, but is obviously hanging by a wire as it swings freely in front of the door.
Continuity mistake: In the scene where Harry tells Marv to go down to the basement door, Marv slips on the icy stairs and falls down to the bottom of the stairwell. At the bottom of the stairs from the camera shot from above you can see an accumulation of snow on the stairs and in the bottom stair well. Yet when Marv finally opens the door and enters the basement all the snow that had accumulated in the stair well has now disappeared.
Revealing mistake: When Kevin rides the rig on the rope to get to the treehouse, you can see that it was a stuntman who is much taller than Kevin and looks nothing like him.
Continuity mistake: Kevin goes out to cut the top off a tree to use as a Christmas tree. The tree top he drags in is much smaller than the one he decorates.
Revealing mistake: As Kevin is flying off the front porch on the toboggan, you can see the small wheels mounted on the bottom of the sled to aid in its "jump".
Continuity mistake: In the scene where Kevin is hanging up ornaments on the Christmas tree and he sees Harry peeping through the window by the reflection of the ornament, the reflection is not entirely accurate. It shows Kevin facing the camera with both the tree and window behind him. The reflection should have shown Kevin with just the window behind him and slightly to his right, based on his original position.