Continuity mistake: When Robbie and Julia are making their friend the limo driver run through the obstacle course to prove his driving ability, you can clearly see both right-side hubcaps come off the car. Then, just a few seconds later, the hubcaps are back on the limo.
Factual error: In the scene where we first meet Rosie, it opens with a shot of the house and then goes inside, passing by some pictures of Rosie and her husband. One of them, a picture of their wedding, says "Frank and Rosie - Wedding 1948", but then when Rosie is talking about how her husband will know how much she still loves him after all those years, Robbie says that he hopes that he and Linda will be as happy as Rosie and her husband on their 50th anniversary. If they got married in 1948, they would be closer to their 40th wedding anniversary. Since the movie is supposed to take place in 1985, this would actually be their 37th wedding anniversary.
Continuity mistake: At the cake shop for Glen and Julia's Wedding, Adam Sandler is feeding Boy George some samples of cake. First you see 2 pieces of cake on the plate. Then he feeds one to that weird person, and in the next frame with the plate it's empty. Then after that there is still one piece of cake on the plate.
Continuity mistake: When Robbie (Adam Sandler) is lying in the trash dumpster, after he just got dumped, you can see him covered with trash. Then the camera switches to Julia (Drew Barrymore), and when it goes back to Robbie, there's different trash, and less trash, and it isn't in the same position.
Continuity mistake: During the 50th wedding anniversary party, after Rosie is done singing, she walks over to her husband Frank and they embrace with her on the left, and him on the right. The camera cuts away to Adam Sandler, then back to them, only now Frank is on the left and Rosie is on the right. The camera cuts to Adam again, then back to the couple where they are in their original positions.
Audio problem: In the scene where Robbie is sitting outside and Linda walks up to him to tell him about why she called the wedding off, she firstly walks on the concrete and you can hear her footsteps, then she walks on the grass, but you can still hear her heels clicking.
Continuity mistake: In the scene where Sammy swerves his limo around the cones, when he stops to pick up the dummies, the limo is not in-line with the cones, in the next shot, it's perfectly in-line, then it changes back again.
Continuity mistake: At the first wedding, the left hand side (as we look at it) of the bow tie that the brother of the groom is wearing, keeps appearing and disappearing from his collar.
Other mistake: After the on-board announcement that the plane is at cruising speed and altitude, the exterior shots still show the wing flaps extended for landing. Due to structural limitations and the extra drag created, the flaps cannot be used at higher speeds.
Factual error: Throughout the whole film you hear Julia saying her wedding is "Sunday August 5". This movie was set in 1985, and August 5 was a Monday in 1985.
Continuity mistake: In the scene where Robbie and Julia are practicing her wedding kiss, her necklace and hair shift position on each shot.
Continuity mistake: At the first wedding he is singing at, the best man comes up and talks, the microphone stand moves into different positions. In one shot it is facing forward and the next it will be backwards. It goes back and forth the whole time.
Continuity mistake: In the scene where Sammy is driving around the orange cones in his limo, he has to pick up a dummy of a bride and groom. In the first shot, there are no dummies there, but in the next shot there are two dummies waiting to be picked up.
Continuity mistake: In the first wedding for the Veltrys, George finishes "Do you really want to hurt me" as Julia walks into the kitchen after having her bum pinched. Then the next scene is Robbie telling the drunk boy outside to go in, and in the background is George re-finishing "Do you really want to hurt me". Then George starts the song again as Robbie is not there. The intro is quite long to this song, but then the scene goes back to Robbie outside still helping the boy and the background noise is the middle of "Do you really want to hurt me." This is not possible.
Continuity mistake: In the scene where Robbie is lying in the bin outside and he is talking to Julia, there is a round sort of plate or dish lying next to his right shoulder - in the next shot it is on his left side near his stomach, and in the next shot it is back again.
Continuity mistake: When Robbie is singing at his first wedding back (Cindy and Scott's), just after George sings the backup "Holiday", Robbie then sings "It would be.." and when he sings this he lifts his left hand into shot and on his ring finger you can see something white in a ring shape around the top part of that finger, but in the next shot of him after it changes to a shot of the annoyed father and back, the white "ring" that was around his finger is no longer there.
Continuity mistake: The back ground colour outside the banquet hall keeps changing, in the first scene there is a sign, in the next it's gone.
Factual error: Although the movie is set in 1985, the first exterior shot of the airplane shows an A320 (note the winglets) which didn't enter service until 1987.