At the New Year's Eve party at end of the film when Harry is telling Sally all the things he loves about her, people in the background are still seen dancing even though the music has stopped and you hear the crowd counting down to midnight.
When Harry and Sally enter the diner in 1977, the credit card sticker on the door reads MasterCard. At the time, the company was still known as MasterCharge and the current name was adopted only in 1979.
When Jess gives a speech at the wedding he says: "If Marie or I had found either of them remotely attractive... we would not be here today." The first half of the sentence does not match his mouth movements.
When Harry and Sally are in the museum, Harry makes a joke about hieroglyphics being part of an ancient comic strip. When he says "...about a character named Sphinxy," his lips don't match the words he can be heard saying.
When visiting their friends and helping to serve dessert, Sally tells Marie that "Harry hates sweets." However, on New Year's Eve, Harry is alone and eating a bag of "moon pie" chocolate cookies, telling himself they are the best in the world.
When Sally tells Harry that she's watching Casablanca, she says it's on channel 11. A few moments later, when they're both watching the movie in their respective apartments, both TVs are turned to channel 7.
The first time Harry and Sally stop at a diner (on the way from Chicago to
New York), Sally opens the menu, but on the next shot, she opens it again. Her hands are in different positions depending on the camera angle for most of the sequence.
When Harry and Sally are in the diner talking about whether the women have a good time in bed with him, the bite mark in Sally's sandwich keeps moving from being near the side, to the centre, and back to the side.
In 1977, when Harry and Sally enter the diner and also while they eat, Sally's hair is limp and untidy. When Sally is tallying the bill, it is neat freshly styled. When they go outdoors, her hair is untidy again.
The morning after Harry and Sally make love all four of them are on the phone reporting the incident. Jess and Marie are in bed on their respective phones. Harry and Sally are montaged on either side of the bed. There is a mirror behind Harry. A man can be seen crossing left to right in the mirror who is part of the crew.
When Harry and Sally drive from the University of Chicago to New York, they should drive on the Lake Shore Drive heading to the south (to the direction of Gary), not to the north (to the direction of downtown). So they should not be on the Lake Shore drive on the north of downtown.
When Sally is faking the orgasm in Katz's Deli, the woman who says "I'll have what she's having" is seated in the self service section and a waiter would not have come over to take here order. The waiter service section is against the wall to Sally's left.
When Jess and Marie are talking to Harry and Sally after they make love, a person walks back and forth in the mirror behind Harry. The person is not a crew member but a restaurant worker as you can also see canned food on shelves.
When Harry and Jess are talking in the crowd at the Giants vs Lions game, the overhead shots of the crowd doing the wave is not at the Giants stadium. It is actually the Rich Stadium, the home of the Buffalo Bills; now known as Ralph Wilson Stadium.
When Harry is watching New Year's Rocking Eve, the channel on the TV is set to 3 instead of ABC's New York affiliate's channel, 7, revealing that he's actually watching a video tape of the show. In the age of VHS, channel 3 was almost exclusively used to connect VHS players to TVs.
The goof item below may give away important plot points.
After Harry and Sally have sex, Sally is getting up for some water and is supposed to be naked, however as she stands to put on her robe, you can see her night gown around her legs, which must be tied up around her neck under her hair.