This is the first movie in the American Pie franchise that you see Stifler and his mother communicating with each other directly. In the first movie he walks in on her and Finch, but only you only hear Finch's voice , every other time , Stifler either references her, or he's not around when she turns up.
Chris Klein did his own dancing for Oz's "Celebrity Dance-Off" routine. Klein went to dance workshops with choreographers as well as adding his own moves to fit with his character. However, his routine was shortened in the final cut.
In the first spinoff film, American Pie presents: Band Camp, Chuck "The Shermanator" Sherman (Chris Owen) is revealed to have become a guidance counselor at East Great Falls High. Whether or not he still is by the events of this film is neither confirmed nor denied. Also in the same film, it is mentioned several times that Steve Stifler (Seann William Scott) became a filmmaker/producer in the adult film industry. But seeing as how he is a temp in this film, it's possible that he may have changed careers between the events of Band Camp and American Reunion.
During the scene where Jim is talking to Kevin on the phone about the East Great Falls Class of 1999 Reunion. Kevin tells Jim to check the Facebook page and the number of "maybe attending" RSVP's is "69".
In all four films, the films begin with an embarrassing moment involving Jim, getting caught out in an sexual act by a family member. American Pie Jim's parents catch him masturbating with a tube sock, in American Pie 2 Jim's parents catch him having sex, in American Wedding Noah catches Jim being given fellatio by Michelle, and this film with Jim's son Evan catching Jim masturbating.
When Stifler meets Finch's mom (played by Rebecca De Mornay) for the first time at the reunion, she says, "Are you ready for me, Stifler?" She famously used a similar line in Risky Business (1983) with Tom Cruise. Playing prostitute, Lana, she says, "Are you ready for me, Ralph?"
Though they both appear in all the theatrical films in the "American Pie" series, this marks the first time that Jennifer Coolidge and Eugene Levy share any scenes together. In real life, the two actors are frequent co-stars and friends.
This is the fifth time Eddie Kaye Thomas, 'John Cho' and Neil Patrick Harris (cameo appearance) star in a film together. Although Harris had an uncredited cameo in "American Pie 2", "American Reunion" is the fourth film written by Jon Hurwitz and Hayden Schlossberg to include the three actors after the "Harold and Kumar" films.
Michelle Flaherty (Alyson Hannigan) is the only main character without any reference to any kind of job occupation. It is not even revealed if she's an housewife. -Jim works for Katz Lewn & Soben Advertising. Although it is never mentioned what his actual job is. Stifler is a temp at JB Global and is offered to become a professional party planner later in the movie. Oz is a sportscaster. Kevin is an architect. Finch eventually reveals he's an assistant-manager for Staples. Vicky has been working for the same company in New-York for the last 10 years, although the nature of her job is never mentioned. Heather works at a hospital but her job title is never specified. Ron is a cardiologist. Selena is a barmaid and Mia is a model.