Early on, South Park (1997) creators Trey Parker and Matt Stone were lined up to write the prequel for $1.5 million. They later decided to not work on the project and returned all of the money to New Line.
In one scene, Lloyd is looking at a pottery magazine, sees a large jug, and says to Harry, "Your mom has jugs like these!" to which Harry replies, "Yeah, but hers were never in a magazine." In fact Mimi Rogers, who plays Harry's mother, posed for Playboy in 1993.
Eric Christian Olsen was repeatedly denied the role of Lloyd because the producers thought he was "too good-looking". It was only after seeing some home-video footage of Eric in full make-up improvising a scene with already-cast Derek Richardson that they gave him the role.
The scenes in which the boys go on a field trip to a natural history museum were filmed in the lobby of the Healey Building, a historic neo-gothic high-rise in Downtown Atlanta, Georgia, which has never been a museum. Several other scenes were filmed in the immediate area of the building.
In the film it is established Harry is born in 1969 and Lloyd is born in 1970, which means in the film which takes place in 1986, Harry is 17 and Lloyd is 16. In Dumb and Dumber (1994) which takes place 8 years later, Harry is 25 and Lloyd is 24.
Jessica's Dad freaks out when he finds the bathroom is covered in melted chocolate which melted in Harry's pocket and Jessica's Dad thinks it is poo. This foreshadows Lloyd spiking Harry's coffee with laxative out of revenge and Harry is forced to poop in a broken toilet at Mary's house in Dumb and Dumber (2004).
Rachel Nichols would later go on to star in Star Trek (2009) which is a reboot of Star Trek (1966) (TV Series). In the film which takes place in an alternate timeline, Rachel Nichols's character Galia is seduced by an alternate younger version of Captain James T. Kirk (Played in the film by Chris Pine). In this film, Jessica (Nichols) flirts with teenage Harry and Lloyd whom soon fight over her.
The trivia item below may give away important plot points.
The twins at the end of the movie are the Felcher twins (one of which is Freda). In Dumb and Dumber (1994), Freda Felcher is the girl that Lloyd slept with when she was dating Harry. "Freda Felcher...from Cranston...yeah I remember...I mean I remember you talking about her"