Continuity mistake: In the scene where Tommy Doyle looks out the window and sees the shape outside of the house across the street, the porch light is off and the jack o lantern is not lit. When he attempts to show Laurie, the next shot of the house shows that the porch light is on and the jack o lantern is lit.
Continuity mistake: In the beginning, when the doctor is talking to the new nurse for Michael in the car, the nurse is smoking a cigarette, but seconds later she has just lit one up. If she smokes one in 45 seconds then lights up another she is one worst chain smoker I've ever seen. (00:08:05)
Continuity mistake: In the scene where Laurie comes downstairs after taking a shower, she is at her front door singing to herself and she is looking out a window directly to the left of the door. Then there is a shot of the front of her house outside and you see her exit through the door that had the window next to it, but there is no longer a window there.
Continuity mistake: When Michael is at Tommy's school, there are cars parked across the street. When he gets in the car to leave, they are gone.
Continuity mistake: Laurie's hair keeps changing throughout the movie. Her hair changes from wavy to straight while she babysits the kids. It is wavy again when she is going to Lindsey's house, and straight again when she is running back to Tommy's house. It stays straight until Michael starts to strangle her,where it becomes wavy again, having been straight in the previous shot. It all ends with straight hair. Surely all of this could not happen in a matter of hours.
Continuity mistake: Michael breaks the passenger front door window on the wagon when he takes car, a short time later when he's driving in town the window is not broken.
Continuity mistake: In the beginning of the film when Michael is walking through the house, the clocks have different times on them. After he walks by the clock in the living room, it says 9:40. Seconds later, it strikes ten times.
Continuity mistake: When young Michael Myers sees the clown mask, Judith's clothing is bunched up together on the floor. When he puts the mask on, Judith's sweater is lying separately from the rest. (00:05:15)
Continuity mistake: When Laurie is in the closet she stabs Michael with the hanger and leaves it up there. When they show all the locations at the end of the movie, in the shot of the living room look near the floor up close - you can see part of the hanger there, even though it was left upstairs.
Continuity mistake: When Laurie, Annie and Lynda are walking home from school, the part where Lynda walks to her house you can see the station wagon on the side of the road behind them. A few seconds later it has moved up the side of the street.
Continuity mistake: At the beginning of the film the Myers' house is within walking distance of the Strode house, both of which are on one side of town, while the Doyle and Wallace houses are on other considering the driving distance Annie and Laurie had to drive to get to them. But at the end of the film somehow the Myers' house is now within walking distance of the Doyle and Wallace houses.