Mistakes:

• The mechanism which makes the Quidditch box shake can be seen when the box falls over.
• As the three children run across the field to Hagrid's hut, Harry says a few lines ending with "... why didn't I see it before?" Hermione is mouthing Harry's lines with him.
• When Harry, Ron, and Hermione are struggling in the Devil's Snare, a puppeteer can be seen on the left of the screen, working at least some of the masses of tendrils.
• During the train journey, Ron's hair is parted in several different places.
• Harry's glasses sometimes have lenses, and sometimes don't, as do Dumbledore's.
• On the train scene, the same hill as well as lake (as seen by the waves in the middle of the water) are seen multiple times.
• The audio of the scene where Harry, Dudley, and Uncle Vernon were struggling with the sudden explosion of letters in the living room is not synchronized with the video.
• When Uncle Vernon looks at Harry's letter from Hogwarts, he says, "Yours? Who'd be writing to you?" Dudley can be seen mouthing the words next to his father.
• At Halloween, Dumbledore announces for the teachers to follow him to the dungeon to find the troll. The next shot is of McGonagall and in front of her you can see the strings holding up the "floating" candles.
• When Harry receives countless acceptance letters from Hogwarts, he fights with Uncle Vernon, saying the dialogue "They're my letters! Give it to me!" Harry's voice is far deeper than the Harry in the rest of the movie, indicating this line was re-dubbed long after main production when Daniel Radcliffe's voice had already begun to change.
• When Hermione runs across the field her bag switches arms.
• In the scene with the flying keys, we can see the string holding up the broomstick just before Harry grabs it.
• When Harry goes looking for a book on Nicolas Flamel in the restricted section he opens up the screaming book to the first page. When the book starts to scream he is in the middle of the book.
• When Harry, Ron, and Hermione just left Fluffy for the first time and walk into their dorm area, we see, under the painting, the feet of someone closing the painting.
• The note that Hagrid gives to the Goblin in Gringotts is wrinkled in one shot, neat and clean in the next, and then back to wrinkled.
• When Hagrid's cabin is shown the windows are so high up that even Hagrid can't see through them while standing on the ground. Later in the film, when Draco Malfoy spies on Hagrid through the window, the window appears to be at his eye level, and he turns and runs away, revealing that he wasn't standing on anything to make him tall enough to reach the window.
• When Harry and Hagrid are walking down Diagon Alley, the same group of people walk past them, in the opposite direction, twice.
• In Diagon Alley, Harry and Hagrid walk past the same cart and storefront three times. In the opening wide shot, they walk past the purple storefront with the yellow moving scissors and the cart of market goods in front of it. Three shots later, the storefront and cart are shown again in detail, as Harry and Hagrid pass. The next shot shows them passing the cart (with a stack of cauldrons in the background). Several shots later, after passing the store with the owls, they are seen once again passing the cart with the same stack of cauldrons in the background.
• Just after passing Madam Malkin's shop and before the owl emporium in Diagon Alley, a woman dressed all in black and a man with a burgandy top hat and mutton chops pass on Harry's right walking in the opposite direction. In the next shot, as Harry looks to his left, the same pair can be seen standing and chatting in the doorway of the owl emporium.
• In Diagon Alley, Harry and Hagrid pass many groups of people multiple times, though they appear to be walking continuously in one direction. Watch for the wizard with curly red hair, the man with a top hat and mutton chops, and the group of three girls who cross in the foreground of the opening shot.
• When Ron gets drooled on by Fluffy and gets wet, but two shots later he's completely dry.
• When the first years climb the stairs and meet Professor McGonagall for the first time, Ron's robe is hanging partly open in one shot, but is closed in the next.
• When Harry and Ron are fighting the troll in the girl's toilet, they use a spell to lift the troll's club over its head and drop it. The club does hit the troll and makes an appropriate sound effect, but then the club falls to the floor, it makes no sound at all.
• During the chess scene, the shadow of a figure can be seen covering a light shining on the chess board near the bottom of the screen.
• When Harry is struggling with his broom in the first quidich game, he almost falls off and is hanging from it. Near the base of the handle a large wire bracket is clearly visible. Possibly to support the rider's feet while riding it. The bracket isn't visible on any of the other brooms, and it doesn't appear on Harry's broom at any other time in the movie.
• During the first flying lesson, Neville's robe is torn by the pointed rod of the statue as he falls down. The tear in his robe caused by the rod vanishes when he falls down.
• When Harry, wearing his cloak of invisibility, spies on Professor Quirrell being bullied by Professor Snape, the shots filmed from Harry's point of view have him at eye level with the adults even though he is clearly shorter than they are.
• In the scene in the hut on the rock, where Hagrid comes to fetch Harry, Harry's T-shirt is hanging off his left shoulder at the beginning of the scene, however, for the rest of the scene, it is covering both his shoulders.
• In their first potions class, Suzanne Bones is seen sitting next to Ron. However, earlier in the movie we see Suzanne Bones sorted into Hufflepuff, not Gryffindor or Slytherin, the two houses in that particular class.
• In the scene following the defeat of the troll, Quirrel is shown speaking with the other professors, at which point they, and the trio, leave the girls' bathroom. Their footsteps are clearly heard as they move down the hall; however, in the next shot of the troll laying on the floor, the sound effects have ceased. In the last shot, of Quirrell jumping nervously in response to the troll grunting, the footsteps can again be heard.