The segments of married couples telling the stories of how they met are real stories that director Rob Reiner collected for the film. Then they hired actors to relay the stories.
The orgasm scene was filmed at Katz's Deli, an actual restaurant on New York's E. Houston Street. The table at which the scene was filmed now has a plaque on it that reads, "Where Harry met Sally...hope you have what she had!"
According to writer Nora Ephron, the infamous "I'll have what she's having" line was actually suggested by Billy Crystal.
The scene where we see all four lead characters talking to each other individually on various telephones took sixty takes to nail.
The concept of Sally being a picky eater was based on the film's screenwriter, Nora Ephron. Years after the movie came out, when Ephron was on a plane and ordered something very precise, the stewardess looked at her and asked, "Have you ever seen the movie When Harry Met Sally?"