Carol Hathaway (Julianna Margulies) was supposed to be brain-dead from a suicide attempt in the first episode, but the character was revived for the series. For the first episode, Margulies was credited as a guest star.
If anything had gone wrong during the broadcast of the live episode, such as a technical failure or forgotten dialogue, the producers had additional actors ready to improvise a scene that would have been inserted to cover. This contingency was never used.
George Clooney had his first regular TV role in a comedy ten years earlier called E/R.
Dr. Romano (Paul McCrane) has a model of an Apollo Saturn V rocket in the background of his office. McCrane played astronaut Charles Conrad, commander of Apollo 12, in the HBO mini-series _"From the Earth to the Moon" (1998) (mini)_
The character played by Ming-Na Wen was addressed only as Deborah Chen when she first appeared in the series in 1995. When she returned in 2000, she took to a more traditional name, Jing-Mei, which was also the name of the character Ming-Na played in The Joy Luck Club.
In the live broadcast of 1997, the baseball game that George Clooney's character is watching in the break room was the Cubs-Astros game, also being broadcast live that night on WGN.
George Clooney's cousin, Miguel Ferrer, appeared as a guest star in the two-hour pilot episode, and Clooney's aunt, Rosemary Clooney (Ferrer's mother), appeared in the second regular episode. Clooney shared scenes with neither of them.
Drs. Mark Green and Elizabeth Corday lived at 1211 Dupont Drive.
Matthew Watkins, the child who plays Reese Benton, Peter's deaf son, is hearing impaired in real life
Frank, the desk clerk (Troy Evans), always talks about life on the "force" as a Chicago police officer. In a very early episode he had an appearance as a police officer who was shot and treated by the ER staff.
In one episode, Dr. Lewis admits that she's only familiar with the Walt Whitman poem "I Sing the Body Electric" because it appeared in song form in the movie Fame. That song in that film was sung by Paul McCrane (Dr. Romano).
The character of Dr. John Carter was named after the protagonist in the classic "John Carter: Man from Mars" pulp sci-fi stories. Michael Crichton, like many sci-fi writers, considers it an early influence.
The basketball hoop found outside the ambulance bay of the ER was actually George Clooney's idea. Apparently the actor likes to unwind in between takes by shooting some hoops. Because this, it was placed in an area of the Warner Brothers (Burbank, California) studio lot where it could be picked up by the camera. It quickly became a part of the series itself.
The registration number of the hospital helicopter is N365UC.
Vondie Curtis-Hall appeared on the show as two characters. In season one he played a transsexual (for which he was nominated for an Emmy) and in later episodes played Carla's husband and fought Dr. Benton for custody of his son, Reese.
The character portrayed by Leslie Bibb, Erin Harkins, was originally supposed to die in the episode where she and Luka (Goran Visnjic) were in a car accident. The producers changed their mind after the episode had been written, and after an ambiguous ending, she resurfaced a couple of episodes later, alive and well.
Dr. Carter's date of birth is 4 June 1970. Noah Wyle's in 4 June 1971.
Noah Wyle was the last member of the original cast to leave, at the end of the 2004-2005 season. He will appear occasionally in future seasons. Sherry Stringfield is also an original cast member, but she left for 5 seasons, which made Noah Wyle the only cast member to be on the show every year for the series first eleven seasons.
In the episode where Dr. Romano is showing his prosthetic arm to the staff at the desk, one of the other doctors refers to him as "Robodoc". Paul McCrane played one of the bad guys in RoboCop.
The helicopter used for ER actually belongs to the University of Chicago Hospital.
Including Gloria Reuben and CCH Pounder (who appeared as recurring guest stars during the first season), the original cast combined for 25 nominations in the Leading and Supporting Acting categories at the Emmy Awards from 1995-2000. Julianna Margulies (Best Supporting Actress, 1995) was the only one to ever win.
The first four episodes of the show all began the same way, with one of the doctors being awakened early in the morning from "Exam 8" at the end of the hallway in this order: Greene (Pilot), Lewis (Day One), Benton (Going Home), Carter (Hit and Run). This became a recurring motif throughout the run of the series, and the 200th episode began this way as well. Of the original five doctors, Ross (George Clooney) was the only one who was never shown sleeping in Exam 8.
Doug Ross frequently hung his head low, appearing ashamed or thoughtful or privately amused, depending on the scene. This wasn't just an element of the character: George Clooney had taken to writing his lines on papers, sheets, and other props (especially that complicated medical terminology).
The set for the pilot episode was a rundown hospital in East Los Angeles, as they couldn't afford to build a proper set of their own. As the rooms were quite small, this necessitated the use of the Steadicam, which has since become the trademark of the show. Real members of the public, usually Punk gangs, would often pull up outside, mistaking the set for the real thing.
Alex Kingston announced in an interview in 2004 that her contract to return for an eighth year on the show was not renewed. She said she was told plots for her character had "run their course".
Although mostly shot at Warner Brother's Burbank soundstages, the cast and crew usually will make at least two trips to Chicago each season to shoot realistic exterior scenes for several episodes which include many familiar Chicago landmarks. These scenes are normally shot on early Sunday mornings to avoid disrupting traffic.
Producers wanted the character of Carol, played by Julianna Margulies to switch from being a nurse to a doctor and even filmed episodes of her starting medical school. Margulies objected to the idea, saying that her character would be so proud of being a nurse she would never want to change, so the idea was dropped. Years later, the character of Abby, played by Maura Tierney did go from being a nurse to a doctor.