Continuity mistake: When Randy answers the phone he kneels down putting his head about level with the top of the TV, yet when Sidney goes to drop the TV on Stu's head the TV is much higher.
Continuity mistake: After Courtney Cox runs to the van when she's being chased, she hops into the van and throws it into reverse, guns it, then slams on the brakes, and the body falls down onto the windshield. Slamming on the brakes after going in reverse would cause the body to fall the other way, toward the back of the van. (01:22:50)
Continuity mistake: When Drew Barrymore is running to the kitchen after the patio windows break she grabs a knife. When they show her going through the doors from the inside to go outside her knife's curving blade is pointing toward the celling but when the show her leaving the house through the doors from the outside the knife curve blade is pointing down.
Audio problem: When Steve is on the porch and gagged, the killer instructs Casey to turn off the lights. Steve shakes his head and lets out some muffled 'No's. When the lights go out he says one last 'No' but you can still tell he isn't saying it. Even though his mouth is gagged, he makes no body movements to correlate with his shouts like he did before, especially not his jaw. Despite it being dark you can still tell. (00:06:10)
Continuity mistake: When the principal comes back into his office after checking out who was knocking on his door you can see a closet in the background with coats in it. When they change the angle the jackets have moved to a different position. (00:50:35)
Continuity mistake: When Sidney and Billy are talking in the bedroom at Stu's house, when the camera is on Billy, Sidney's hair is in a different position than when the camera is on her.
Continuity mistake: At the end when Sidney is in Dewey's police car and the killer is there, she opens the door and falls out but the door is still locked. In some cars you can open the door when it is locked but the lock always pops up after you open the door, and this one didn't.
Plot hole: Given the magnitude of the crimes that occur at the house at the end, the police can be seen in the last shot dusting Dewey's truck. If the police are so careful as to dust for prints when the entire rest of the crime scene is heavily contaminated by everyone from the EMTs, Gale doing her news, police, etc. makes what they are doing seem silly.
Continuity mistake: After Casey has been stabbed in the chest she falls down and the killer gets on top of her, before he can stab her again she knocks the knife out of his hand and the killer instead starts to strangle her. She then kicks him off her but you can see he still has the knife in one of his hands as he falls backwards. (00:11:00)
Visible crew/equipment: When Casey agrees to play the killer's game she crouches down next to the television and as the killer says "Here's how we play..." you can see a clear shadow of the head of the boom microphone cast on the white wooden railing at the top right of the screen. (00:06:25)
Audio problem: At the party, Gale places a portable small camera on top of the TV to spy on the teens there. Later, the teens are watching the Halloween movie on this very TV and talking loudly. The movie is playing with sound when they are watching it. However, when we see Gale and Kenny's perspective as they are watching the feedback, they can hear the teens talking. However, despite the camera sitting right on top of the TV, it doesn't pick up the audio from the movie playingr. This mistake is repeated not long after when Ghostface is sneaking up behind the one teen left behind on the couch who's watching the movie at an even louder volume.
Audio problem: After Sidney and Billy have their fight in the hallway after he's released, the scene cuts to Mr. Himbry reprimanding two students wearing the Ghostface mask. He takes some scissors and starts to cut them up and waves the scissors around. The entire time, the scissors are making very loud, very distracting and unrealistic "SHING" sounds like metal swords sliding against each other in a hallway. These scissors simply would not make such obnoxious sounds with the simple movements he's doing with them. They even make the sound as he's cutting through the mask, which if anything would have muffled the sounds they made even more.
Other mistake: After Billy Loomis and Stuart "Stu" Macher are revealed as the villains, they stab each other multiple times to appear as victims. Billy cuts Stu too deep, and Stu begins feeling weak and bleeding profusely from his wounds, showing that he may be dying. When Sidney (in the Ghostface costume) stabs Billy with the umbrella, Stu's rage takes over and he suddenly has the dangerous energy to battle Sidney in the living room. Stu nearly kills Sidney, until she pushes the TV on his head. If Stu was dying in the kitchen, how does he have all that energy to fight Sidney?