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.
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 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.
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.
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.
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.
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.
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.
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.
There was an entire sub-plot involving Healy's friend, Sulley (Jeffrey Tambor) that was cut from the original release. This is why, despite prominent billing in the opening credits, Tambor only appears in two brief scenes. Here, Sulley is a policeman and recovering drug addict/alcoholic. He has been clean for 19 months, however, after being re-acquainted with Healy he returns to drugs and is eventually eaten by his own pet python. This sub-plot is reinserted into the Extended Cut.
Brett Favre's scene was filmed just 2 weeks after playing in Super Bowl 32. The San Francisco 49ers were the team the Green Bay Packers beat in the NFC championship game. Mary said she was a fan of the 49ers in the film.
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.
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.
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).
When Tucker (Norm) is describing Pat Healy's fake arrest record he refers to murders in Utah and Washington where in the 1970s serial killer Ted Bundy stalked and murdered young women. Bundy also killed female college students in a sorority house at Florida State University. Norm later refers to Ted, Ben Stiller's character, as 'the biggest stalker of us all'. Ted himself picks up a hitchhiker who is a serial killer on his way to Florida.
Warren gets beaned while in the batting cage and gets his left eye blackened. later, Ted announces he got a ball for him signed by Tony Conigliaro. Conigliaro got beaned, a broken left eye socket that effectively ended his career.
During the batting cage incident Warren gets beaned which results in a blackened left eye. Later Ted says he got a baseball for Warren signed by Tony Conigliarlo. Conigliaro suffered a beaning that virtually ended his baseball career. He also had a blackened left eye.
First Ben Stiller film with a character name Norm under the fake name Tucker (Lee Evans), second film was Meet the Parents (2000) in which the interrogating officer name is Norm, both characters have a hostile conversation with Stiller's character.