Seann William Scott improvised some of his dialogue, this can be observed by his cast mate's reactions in some scenes, such as when he tells Jessica he wants to know how many women she has slept with that year - Natasha Lyonne's amused reaction is genuine, she isn't acting.
Eddie Kaye Thomas was laughing so hard at Seann William Scott's antics during the lesbian scene that he had to be cut out of a lot of the shots. This is why these scenes contain a lot of shots of just Stifler and Jim, even though Finch is supposed to be standing right next to them.
In the scene when Alyson Hannigan (Michelle) is "breaking up" with Jim, her hair is styled differently than normal. This is because she was shooting an episode of Buffy the Vampire Slayer (1997) and she ran over to the set during a break.
The "lesbians'" house in reality is across the street from the house used in Ferris Bueller's Day Off (1986).
Fearing typecasting, Shannon Elizabeth declined to perform a nude scene for this sequel.
The movie originally included scenes featuring Stifler's dad (played by Chris Penn). These were removed after negative reaction in test screenings.
Nadia's first scene was actually shot in downtown LA, not New York. The World Trade Center towers were composited into the skyline. Yellow cabs and hot dog vendors were added for effect.
The band 3 Doors Down recorded an alternate version of their song "Be Like That" for the soundtrack. The first 2 lines were different than the version on their album "The Better Life".
The classroom used in the opening scene where Chris Ostreicher (Chris Klein} and Steve Stifler (Seann William Scott) are getting ready to take a final exam is the same one used in Old School (2003) when Frank Ricard (Will Ferrell) is getting beaten up by Dean "Cheese" Gordon Pritchard (Jeremy Piven).
Joseph D. Reitman (Male EMT) and Shannon Elizabeth (Nadia) were married in real life in 2002.
The scene where Nadia calls Jim from a payphone was filmed at the same location as Kyle Reese's arrival in The Terminator (1984). That film also featured Bill Paxton (as one of the punks. The one who says, "this guy's a couple cans short of a six pack"), who was considered for the role of Stifler's dad in a deleted scene.
Adam Herz, the writer of this film, wrote the screenplay with numerous references to the University of Michigan (his own alma mater). He also included Michigan's fight song, "Hail to the Victors", in the movie. However, the university did not approve use of its name, due to the adult nature of the film. Herz had to omit any reference to the school.
Bill Paxton (who appears in The Terminator (1984) as one of the punks) was originally cast as Stifler's dad but had to leave the project due to his schedule. One of the characters in the franchise is named Chuck Sherman who calls himself "The Shermanator".
Producer Craig Perry stated while promoting American Reunion that John C. McGinley auditioned for the role of Stifler's Dad (a part that was eventually cut from the finished film) and Ashlee Simpson auditioned for the role of Christy.
The zip code shown on the post card to Jim from Nadia is for Spring Lake, Michigan.
J. B. Rogers, who served as the director of this film, also served as the first assistant director on the first film.
Missing from the theatrical release is a scene showing the band camp leader with a rash around his mouth, the morning after having played the trumpet that was inserted into Jim's ass.
The phrase "It happens to the best of us" is said to Jim twice. First by his dad then again by Finch. See quotes.
The Lisa Arturo scene has been compared to the Barbara Crampton-Kathleen Kinmont nude scene in Fraternity Vacation (1985).
The first of two movies in the franchise that would quote Star Wars: Episode IV - A New Hope (1977). This would happen again in American Reunion (2012).
When Stifler barges into the bedroom at the lesbians' house that the guys are painting to announce that he discovered a dildo, a poster of Melissa Etheridge is on the door. Melissa Etheridge is a lesbian which could be why the girls were fans.
The radios that Finch, Jim, Oz, & Stifler are using are either FRS or GMRS radios. Consumer 2-way radios that transmit ½ watt or 5 watts (respectively) and do not require a license. They have declined in use for the same reason that payphones have: Proliferation & ubiquitousness of cellular telephones.