Julia Roberts (Dr. Rachel Mannus) and Kiefer Sutherland (Nelson Wright) started dating during filming. They ended up engaged, but Roberts ultimately broke it off. She later married Lyle Lovett.

During pre-production, the actors worked with medical technical advisor Ruth F. Ekholm, who tutored them on the proper medical procedures for the scenes in which the students flatline on the EKG and EEG machines, signaling cardiac and brain death, respectively. They also took advantage of Peter Filardi's research of published accounts from people who'd had near-death experiences. Almost all accident victims reported a tunnel leading to a beautiful white light and friendly voices. People who had attempted suicide had troubled, emotionally painful near-death experiences.

Val Kilmer turned down the role of Nelson Wright.

Nicole Kidman was considered for the role of Rachel Mannus.

One of a handful of films in a mini-cycle of Hollywood pictures all released in 1990 that dealt with the theme of after-life and near-death experiences which all got released seven years after Brainstorm (1983). The films include Ghost (1990), Flatliners (1990), and Jacob's Ladder (1990).

The Washington Post described this picture as "a Brat Pack neo-Gothic that plays like 'Frankenstein' in reverse".

Kevin Bacon was cast as the idealistic, yet pragmatic David Labraccio, who provides the voice of reason for the other experimenters, and who tries to right an old wrong committed in his childhood. Joel Schumacher said: "Labraccio is the opposite of Nelson Wright (Kiefer Sutherland). As the movie progresses, everyone becomes dependent on Labraccio, as a kind of center to hold them all together, especially Nelson."

In later years, Joel Schumacher admitted that he felt he was the wrong director for Dying Young (1991). Schumacher said that he only did it as a personal favor to Julia Roberts, as he had loved working with her on Flatliners (1990).

This is the second of five collaborations by Kiefer Sutherland (Nelson Wright) and director Joel Schumacher. They had previously worked together in The Lost Boys (1987), and would later work together in Twelve (2010), Phone Booth (2002), and A Time to Kill (1996).

Following a brief period of rehearsals, Joel Schumacher assembled the film's cast and crew in Chicago on October 23, 1989. For two nights, the Museum of Science and Industry was used as the ominous exterior of the Taft Building. For the exterior of the university campus, the production selected the scenic Lake Shore campus of Loyola University.

Kiefer Sutherland described this as "The Breakfast Club Dies" and "St Elmo's Funeral" jokingly in a Fangoria interview.

Among the many sets constructed on three sound stages at the Burbank studios was the interior of the university's Taft Building, a huge, elaborate structure that contained an ornate hallway and the dog lab in which the five students conduct their experiments. Joel Schumacher, Jan De Bont, and Eugenio Zanetti all created a Gothically stylized atmosphere in the lab by incorporating ominous lighting beneath an iron-grid floor, all to evoke images of the underworld, while angels and guardians above the columns suggest divine protection.

Kiefer Sutherland said of his Nelson Wright character in this movie: "My attraction to the character was that he had an incredible passion for what he did, and for what he believed, and that kind of conviction is always a very appealing thing to play."

Julia Roberts said of her Dr. Rachel Mannus character in this film: "All five people in this movie have a different reason for wanting to do this. My character is almost obsessed with the idea of death, and making sure that when you die you're going to a good place." Moreover, Roberts said of the film: "Everybody has experienced loss, and wished they had said something, or done something they didn't get a chance to. This movie is about finding those opportunities".

After two weeks of shooting in more than twelve locations in Chicago, Illinois, the production traveled to Burbank, California, to film on the Burbank studios lot. Principal photography was completed on January 22, 1990.

Although they appear to be playing medical students at the same stage of their studies, Kevin Bacon (David Labraccio) was many years older than the rest of the main cast.

Joel Schumacher was intrigued by the spiritual and horrific aspects of "Flatliners", and enthusiastic about the possibilities of creating a visually exciting film. Schumacher said: "Flatliners (1990) is a story about atonement and forgiveness involving these students who, in a sense, violate the gods and pay a price. I think we would all like to know what's in store for us after we die. There have been thousands of reports from all over the world from those who have encountered 'near death', and most of them have reported pleasant experiences. Our movie, however, is saying that you're not to tamper with death. If there is anything we're supposed to learn about it, it will be revealed when we die."

Kevin Bacon's film debut twelve years earlier had been in National Lampoon's Animal House (1978), which featured co-star Kiefer Sutherland's father Donald Sutherland.

Rick Bieber and Michael Douglas were impressed with the plot, which began to evolve in the mind of Peter Filardi after a friend had a near-death experience during surgery. Filardi said "I think every writer tries to do something new and fresh, and the idea for 'Flatliners' came about by seeking a new frontier for people of my generation. The West has been done, space has been pretty well charted, and it seemed as though the only frontiers left would come from within ourselves."

To bring visual life to Peter Filardi's screenplay, Joel Schumacher and the producers, Rick Bieber and Michael Douglas, enlisted production designer Eugenio Zanetti and director of photography Jan De Bont. Schumacher said: "I told Eugenio and Jan that I wanted us all to take risks, to create our own world. This isn't a documentary. It's a fable and a fantasy, and in some ways a science fiction movie. So I wanted to surround it with a very visually exciting and interesting world." The intention was to design sets and atmosphere that would symbolically represent man's eternal struggle with death. To invent this world, the collaborative team of Schumacher, De Bont, and Zanetti all combined a variety of historical architectural styles, such as Greek, Roman, Gothic, and Renaissance, with innovative and dramatic lighting.

First of two collaborations of Kevin Bacon and Kiefer Sutherland, with the second film being A Few Good Men (1992).

Oliver Platt, who plays Randy Steckle, uses his ever-present tape recorder to keep a self-serving chronicle of the experiment for his book about his life as a doctor. Platt said of his character: "Steckle starts out as the naysayer, but then he becomes a real cheerleader, making lofty statements about the experiment being the conquest of our generation."

The picture was the first film to be produced as part of the three-year exclusive agreement between Michael Douglas and Rick Bieber's Stonebridge Entertainment and Columbia Pictures. The subsequent titles in the three-picture deal were Radio Flyer (1992) and Made in America (1993), with Douglas acting as executive producer and producer respectively.

The picture got Oscar nominated in 1991 for an Academy Award in the category of Best Sound Effects Editing, but lost out to The Hunt for Red October (1990).

Rick Bieber said of this movie: "I think this film is going to be very provocative. There's no question that we're dealing with a subject matter that does have religious overtones. From the first moment that we saw the script, we were committed to depicting the story responsibly."

Joel Schumacher would later direct this movie's producer, Michael Douglas, in Falling Down (1993). Douglas does not perform any acting duties in this film.

Producer Michael Douglas had previously starred in a film in the same mixed genre in Michael Crichton's Coma (1978).

This film, starring Julia Roberts (Dr. Rachel Mannus), was released in the same year as her massive box-office hit movie Pretty Woman (1990), in which she co-starred in with Richard Gere.

The movie features the up-tempo rock song "Party Town", which was written and performed by Dave Stewart (David A. Stewart) of rock band Eurythmics fame. Arista Records released the song as the first single on Stewart's debut solo album, and as a music video directed by Joel Schumacher, containing footage from this movie.

First of two collaborations of Julia Roberts and Joel Schumacher. They also collaborated on Dying Young (1991).

Debut theatrical feature film of Hope Davis (Anne Coldren), who also appeared in Home Alone (1990).

For cast members and filmmakers alike, the experience was personally enriching, and each came away with a deeper understanding and affirmation of life.

Though the movie featured a cast of young American actors, none of them were members of the so-called group of 1980s actors and actresses known as "The Brat Pack", many of whom had starred in Joel Schumacher's earlier picture St. Elmo's Fire (1985).

One of several movies starring Julia Roberts (Dr. Rachel Mannus), that have been scored by James Newton Howard.

Debut produced screenplay for a theatrical movie of writer Peter Filardi.

The film's title refers to "flatlining", which show-business trade-paper Variety defined as "the lack of vital signs (which) produces a flat line on EKG and EEG monitors."

William Baldwin and John Duda were both also in Backdraft (1991), and in each film, Duda, a child actor, played a younger version (shown in some kind of flashback) of one of Baldwin's co-stars (Kevin Bacon here and Kurt Russell in Backdraft).

Film debut of actress Patricia Belcher (Edna - Ward Nurse).

Debut theatrical feature film as a producer for Rick Bieber.

Kiefer Sutherland (Nelson Wright) and Tom Kurlander (Medical Student) also worked together on Young Guns II (1990) as Doc Scurlock & J.W. Bell respectively.

Julia Roberts still has the original prosboscis she started her acting career with. She had it altered some time between The Pelican Brief (1993) and I Love Trouble (1994).

Lighting in the movie is a significant predictor of what will happen in the scene. A deep orange color is usually a sign of promise and positivity, while blue usually means something bad will happen.

Billy Mahoney's (Joshua Rudoy's) death is an in-joke to filmmakers, where the three acts of a story are frequently described as: 1) You put a character in a tree. 2) You throw rocks at him. 3) He somehow gets down from the tree.

When David Labraccio (Kevin Bacon) goes to visit Winnie Hicks (Kimberly Scott) to atone for taunting her, he mentions that they both went to S.B. Butler School as kids, to remind her who he was. Peter Filardi included this as a nod to his hometown in southeastern Connecticut, where there is a real S.B. Butler Elementary School, near downtown Mystic, Connecticut.

Steckle is the only main character to never be flatlined and confronted with his past.

William Baldwin played Joe Hurley, the handsome lady killer whose sexual conquests come back to haunt him, and who must "face what he has done to the young women who have trusted him" Joel Schumacher said.

The night of David's attempt at 2:20, Randy mentions that it's Halloween and a full moon. This would mean the movie either took place in 1974 or 2001.