The scene with the homosexuals is staged in a South Carolina Rest Stop (with South Carolina trooper decals and uniforms). This is based on a real case where Troopers discovered that the stops were being used as meeting places for homosexuals to have anonymous sex. The troopers learned this after arresting a South Carolina state official "in the act" at one of the stops.
After the financial losses suffered from Kingpin (1996), the Farrely brothers thought their next film would probably be their last. So they decided to go all out and deliver the most hysterically black comedy they could dream up. When There's Something About Mary (1998) became a box-office smash hit, the Farrelly's careers were safe to continue.
Lee Evans' British accent in the movie was characterized by a film critic as quite possibly the worst fake British accent in a movie he had ever heard. Lee Evans' is in fact British. However the accent he used in this film was overly exaggerated for the role.
The studio was initially reluctant to allow Ben Stiller - the Farrelly Brothers' first choice - to star, so the brothers decided upon a then unknown Owen Wilson instead. When the studio was even more reluctant to let Wilson star, they agreed to allow the Farrellys to cast Stiller.
The dialogue between Mary and Ted about how there aren't enough meats on sticks was originally written for an episode of Seinfeld (1989) that never aired. The Farrelly Brothers liked it and bought it for use in the movie.
Cameron Diaz's father was on set during filming, so the Farrellys decided to throw him in the movie. In the scene where Ben Stiller is released from prison after being wrongfully accused of murder, Cameron's dad is the inmate in the front with a beard and long hair jeering at Ben.
The waterfront house in which Mary lives in Miami was destroyed in 2008 by a construction accident that killed two people and injured five others. A crane collapsed at a nearby 40-story condominium under construction going through the roof of the house. The developer had originally designed to incorporate the house to be part of the property of the condominium development. As a result of the accident and the 2008 housing recession, the condominium never opened.
One detective in the scene at the police station with Ben Stiller says, "I'm Detective Stabler, this is Detective Krevoy." These names are a reference to the film's producers, Steven Stabler and Brad Krevoy.
There is an entire sub-plot cut from the original release involving Healey's friend, Sulley, where he is a Policeman and recovering drug addict/alcoholic. He has been clean for 19 months, however, after being re-aquainted with Healey he returns to drugs and is eventually eaten by his own pet python. This sub-plot is reinserted into the Extended Cut.
Ted brings Warren a baseball autographed by Tony Conigliaro. Conigliaro played for the Boston Red Sox in the 60s and was seriously injured when he was hit in the face by a pitched fastball, echoing Warren's accident in the previous montage.
The high school scene in the beginning was shot at Plantation's City Hall in Florida. Upon seeing a rough cut of the film, and displeased with the raunchiness, city council members requested that Plantation not be acknowledged in the credits.
The character "Patrick Healy" is also the name of an associate producer involved with this film. It is also the name of the National District Attorneys' Association spokesman in the book, "Fear and Loathing in Las Vegas" by Dr. Hunter S. Thompson.
Although the identity of Brett Favre as Mary's previous boyfriend "Brett" is kept secret throughout the film, a clue to his identity is provided by Mary's friend who refers to him as "Pacman". At the time, Favre played for the Green Bay Packers.
The line about Ted mis-pronouncing Brett Favre's last name as "fav-ray" was widely reported to be an ad-lib by Ben Stiller. It wasn't; Stiller is a sports fan who knew the correct "far-v" way to say the name. The Farrellys felt it would be hilarious that Ted would get something that well-known completely wrong.
In the scene where Pat Healy says to Mary, "I just wish they made movies like they used to make. You know, classics like the Karate Kid." Matt Dillon starred with Ralph Macchio, who played the protagonist of The Karate Kid (1984), in The Outsiders (1983).
The dedication at the end of the film is to Ryan Mone who was a young hockey player from Martha's Vineyard. He died in a car accident at the age of seventeen in 1998. The Farrelly brothers are friends of the Mone family and dedicated their film to Ryan as their tribute to his memory.
When Ted goes to pick up Mary for the prom. When Warren is watching t.v., Warren completely solves a Rubix cube. After solving he shouts "Ten Times, Ten Times." Giving the idea that Warren is actually incredibly smart.
Mary says a couple times that she is a fan of the San Francisco 49ers. Retired 49ers quarterback Steve Young was originally asked to play the former boyfriend part that ended up being played by Green Bay Packers QB Brett Favre, but Young declined due to the content of the film.