Chuck Sherman, a.k.a. "The Shermanator" mentions to Stifler that he got married, had a kid, and divorced, and is raising his son "Furlong" by himself. The name "Furlong" is a reference to Edward Furlong, the child actor who played John Connor in Terminator 2.
This film features discrepancies in regards to the spin-off, direct-to-DVD "American Pie Presents" series. In the first spin-off, Band Camp (featuring Steve Stifler's little brother, Matt), Steve was mentioned to be working as a pornographic film director. In American Reunion, Steve is working as a temp at a law firm, and no mention of his previous career is made. Chuck "The Shermanator" Sherman was employed as principal at East Great Falls in Band Camp, but he makes no mention of this at the reunion. No references to the spin-off series are made otherwise.
This is the only American Pie film in the main series to not end with Finch sleeping with Stifler's Mom. Stifler's Mom hooks up with Jim's dad, while Stifler sleeps with Finch's mom.
Chris Klein went to dance workshops and choreographed his dance sequence in the "Celebrity Dance-Off" scene. The host of the show in the film is played by Neil Patrick Harris, who worked with the writers/directors Schlossberg & Hurwitz in the Harold & Kumar series.
Eugene Levy, as Mr. Noah Levenstein (or "Jim's dad"), has starred in all of the American Pie films, including the "American Pie Presents" direct-to-DVD spin-offs, making him the de-facto star of the American Pie franchise (8 films in total).
This is the first film in the American Pie series where both Jennifer Coolidge and Eugene Levy share scenes with one another. They are frequent co-stars otherwise, most notably in Christopher Guest's projects.
Mena Suvari's fifth film with the word "American" in the title. She has had starring roles in American Pie, American Pie 2, American Beauty, American Virgin and now American Reunion. Ironically enough, she also had a guest role in the show American Horror Story.
Of the theatrically released films in the American Pie series, this is the first to be released in a month other than August.