Image: NBC
This well-known actor and comedian made five appearances on ER, playing a character named Jules Rubadoux, better known as Ruby.
Danny Thomas
Red Buttons
Red Buttons appeared five times as Ruby Rubadoux. After a four-episode arc during the show's second season, he returned for one episode during season 11, still angry with Dr. Carter about his wife's death.
Sid Caesar
Milton Berle
Before she worked for President Bartlett in the White House or sipped coffee with the ladies of Wysteria Lane, this actress appeared in a season 2 episode of "ER."
Kathryn Joosten
Kathryn Joosten appeared in a 1996 episode called "A Shift in the Night." Later she played Mrs. Landingham on The West Wing before moving on to "Desperate Housewives."
Teri Hatcher
Stockard Channing
Eva Longoria
Early in her career, this actress appeared on the first episode of "ER"'s fourth season, which gave her good practice for a co-starring role in another long-running medical show.
Ellen Pompeo
Loretta Swit
Kate Walsh
Lisa Edelstein
Lisa Edelstein appeared in "Ambush," kicking off ER's fourth season. Later she played Dr. Cuddy on House and currently stars in "Girlfriends' Guide to Divorce."
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This handsome actor, who has an equally hot brother, visited ER for a three-episode arc during the show's fourth season, and returned to play Dr. George Henry once more during season 11.
Chad Lowe
Rob Lowe's little brother Chad appeared three times in 1997 and reprised his role in 2005. These days he's best known for his role on "Pretty Little Liars."
Ben Affleck
Liam Hemsworth
Owen Wilson
This Goodfella played a dying patient during ER's 11th season.
Robert DeNiro
Ray Liotta
Before he became Henry Hill in "Goodfellas," Ray Liotta played a dying patient in an episode called "Time of Death." The episode combined patient Charlie Metcalf's regrets about his wasted life with the medical details of his last hour of life.
Joe Pesci
Paul Sorvino
What's wrong with a little nepotism when there's so much talent in a family? This famous singer appeared alongside her nephew in "ER"'s third episode.
Rosemary Clooney
Rosemary Clooney was far better known than her nephew George when "ER" hit the airwaves. The talented singer appeared on the third episode of ER's first season, playing a patient who just can't stop singing.
Doris Day
Lena Horne
Ella Fitzgerald
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Everybody has to start somewhere, and this good-looking actor made his television debut on "ER." Now he's known for making American summers both wet and hot.
Chris Pratt
Chris Evans
Chris Pine
Chris Pine's first-ever television credit is for a small role on "ER," back in 2003. Now he's a major movie star, playing Captain Kirk in the most recent "Star Trek" films.
Chris Hemsworth
After he finally got out of Korea, this TV doctor wasn't quite ready to hang up his scrubs, so he signed on for a multi-episode arc on "ER."
Wayne Rogers
Mike Ferrell
Larry Linville
Alan Alda
A few years after "M*A*S*H" ended, Alan Alda put his scrubs back on to play Dr. Gabriel Lawrence on "ER." The five-episode arc aired during the show's sixth season.
Before he transformed himself into a movie star, this actor had a role in a 2000 episode called "Abby Road."
Shia LaBeouf
Years before the "Transformers" movie franchise skyrocketed him to fame, Shia LaBeouf did a series of small parts on television series. One of them was an episode in "ER"'s sixth season.
Patrick Dempsey
Josh Duhamel
Zach Ward
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This adorable child actress is all grown up now, but when she was starting out, she made appearances on "Friends," "Ally McBeal," and a season six episode of "ER."
Marcia McCormick
Dakota Fanning
Dakota Fanning began her professional career at age five. One of her earliest roles was that of a leukemia patient in a 2000 episode of ER.
Hailee Steinfeld
Ariel Winter
Before she became a top cop, this actress appeared in several episodes of "ER" as a nurse who had a major crush on Mark Greene.
Mariska Hargitay
Before she became Olivia Benson on "Law and Order: Special Victims Unit," Mariska Hargitay was Cynthia Hooper, a nurse who pursued Dr. Greene just a little too aggressively. Her episodes aired during the show's fourth season.
Tyne Daly
Heather Locklear
Peggy Lipton
This actress has been a surfer, a nun, and a union organizer, but she also visited County General as Abby Lockhart's mother.
Candice Bergen
Julie Bowen
Meryl Streep
Sally Field
Sally Field has made a career out of playing a mom, including "Mrs. Doubtfire," "Brothers and Sisters," and, of course, "Forrest Gump." She made her first appearance on "ER" in 2000, playing Abby's problematic mother who refused to take the medication prescribed for her bipolar disorder.
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Maybe you remember her as the vet who stole the heart of Tom Hanks in "Turner and Hooch," but she also did a short stint on "ER" as a doctor for human patients.
Sandra Oh
Mare Winningham
Mare Winningham joined ER for a four-episode arc during the show's fifth season. She played Amanda Lee, a doctor who wasn't exactly what she seemed to be.
Kim Raver
Lauren Graham
Before this actor found a home in the White House's west wing, he did a two episode guest appearance on ER.
John Spencer
Martin Sheen
Rob Lowe
Bradley Whitford
Before he came into our living rooms as Josh Lyman on "The West Wing," Bradley Whitford appeared on numerous television shows, including "ER." He appeared as Sean O'Brien in two episodes during the show's first season.
On "ER"'s fourth season premiere, a little-known actor played a guy named Rog. Several years later, he played a guy named Ron who ran a small-town parks department.
Nick Offerman
Nick Offerman had only a couple of television credits on his resume when he appeared in the fourth season premiere of "ER." In 2009, he became a weekly TV presence as the grumpy Ron Swanson on "Parks and Recreation."
Neil Patrick Harris
Chris Pratt
Bob Newhart
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This guy struggled for many years to find the woman who would become the mother of his children. Before that, he appeared on season nine of "ER."
Josh Radnor
Josh Radnor was just starting out when he appeared in a 2003 episode of ER called "The Advocate." Two years later his career took off when he was cast as Ted in "How I Met Your Mother."
Jason Segal
Neil Patrick Harris
Bob Saget
This actress is probably best known for being mad about men, but first she appeared in a four-episode arc of "ER."
Alexis Bledel
Elisabeth Moss
Christina Hendricks
Christina Hendricks played Joyce Westlake, a battered woman who refused to take action against her abusive husband, in a four-episode arc during "ER"'s eighth season. Later we came to know her as Joan on "Mad Men."
January Jones
Before he checked into the "Hotel Rwanda" or moved into the "House of Lies," this talented actor appeared on "ER" as a doctor battling Parkinson's Disease.
Don Cheadle
During ER's ninth season, Don Cheadle appeared as Paul Nathan, a man who decided to take up medicine after being diagnosed with Parkinson's Disease. He works under Elizabeth Corday as he struggles to do his job while battling his physical challenges.
Bob Newhart
Alexander Skarsgard
Jerry Lewis
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Being deaf hasn't stopped this actress from having a busy, successful career, including a 1999 episode of ER.
Renee Zellweger
Jennifer Aniston
Megan Fox
Marlee Matlin
Marlee Matlin rose to prominence in the 1986 film "Children of a Lesser God." In 1999, she appeared on "ER" as a sign language instructor helping Peter Benton learn to communicate with his son, who is deaf.
Now she's a pediatric surgeon on "Grey's Anatomy," but Seattle Grace isn't the first hospital this actress has visited.
Jessica Capshaw
A very young Jessica Capshaw showed up at County General in 1999, making her television debut in an episode called "Rites of Spring." Since 2009, she has played Dr. Arizona Robbins on Grey's Anatomy.
Ellen Pompeo
Chyler Leigh
Sandra Oh
About the same time this actor was getting noticed in "Pulp Fiction," he did several episodes of "ER" as Peter's brother-in-law.
Bruce Willis
Eric Stoltz
Ving Rhames
During "ER"'s first season, Ving Rhames appeared as a mechanic named Walter Robbins. Walter was married to Jackie, Peter Benton's sister.
John Travolta
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Her career was just getting off the ground when this "West Wing" actress appeared in a season one episode of "ER."
Janel Moloney
Before she became the beloved Donna on "The West Wing," Janel Moloney had a small role on "ER." She appeared in an episode called "The Birthday Party" that aired in 1995.
Allison Janney
Stockard Channing
Melissa Fitzgerald
This fiery redhead is better known for her controversial comedy than her acting career, but she landed a guest spot on an early episode of "ER."
Amy Adams
Isla Fisher
Emma Stone
Kathy Griffin
Kathy Griffin has built her career primarily as a stand-up comic, but she has a fairly long acting resume as well. She appeared on the 1995 episode of "ER" called "Motherhood," which you probably remember because that's when Susan's irresponsible sister Chloe gave birth to her baby.
This actress has been an angel, a lawyer and a detective in training, but earlier in her career this actress did a short stint on "ER."
Lucy Liu
Before joining the cast of "Ally McBeal" or the "Charlie's Angels" movie franchise, Lucy Liu appeared in a three-episode arc on "ER." During the show's second season, she played the mother of a small boy who had AIDS.
Calista Flockhart
Farrah Fawcett
Lauren Graham
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Lately she's been busy wrangling her "Modern Family," but in 1998 and 1999, this actress did a stint at County General.
Sofia Vergara
Julie Bowen
During its fifth season, Julie Bowen had a recurring role on "ER." She played Roxanne Please, who was dating John Carter.
Ariel Winter
Sarah Hyland
This striking redhead has done it all, including movies, television and stage work. In 2000, she appeared on "ER" as the estranged mother of one of the doctors.
Judy Greer
Julianne Moore
Frances Fisher
Dr. Kerry Weaver had been given up for adoption as an infant, but in a season 11 episode called "Just As I Am," she finally met her birth mother, played by Frances Fisher. When Mom found out Kerry was gay, however, the relationship ended abruptly.
Debra Messing
After appearing as the drug-seeking girlfriend of an "ER" doctor, this actress went on to inspect crime scenes.
Marg Helgenberger
Marg Helgenberger appeared in a handful of 1996 episodes of "ER" as Karen Hines, with whom Doug Ross gets involved even though she's his father's girlfriend. Might make Thanksgiving a bit awkward.
Marcia Cross
Julia Roberts
Cate Blanchett
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This guy has been making us laugh for decades, including a recurring role as Sheldon Cooper's childhood idol. Back in 2003, he visited County General and became friendly with Susan Lewis.
Milton Berle
Bob Hope
Red Skelton
Bob Newhart
During the show's tenth season, Bob Newhart had a three-episode arc as Ben Hollander, a patient who is fighting both depression and rapidly-progressing blindness. Dr. Lewis took an interest in him, but it didn't end well.
We don't know how she survived that deliberate drive into the Grand Canyon, but a few years later, this actress showed up on "ER" and helped one of the doctors with a medical crisis of his own.
Jane Fonda
Kate Winslet
Susan Sarandon
During the show's 15th and final season, Oscar winner Susan Sarandon appeared as a woman whose grandson died in an accident. When Doug and Carol talk her into donating his organs, a desperately-needed kidney becomes available for John Carter.
Shirley MacLaine
This actress barely survived a tornado in "Twister" and couldn't spare a square for "Seinfeld"'s Elaine, but she found time to appear on ER in 1997.
Jami Gertz
Jami Gertz visited County General in 1997, playing psychiatrist Nina Pomerantz. Some of these characters could definitely use some help in that department!
Helen Hunt
Nicole Kidman
Jodie Foster
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She rocketed to fame by helping a young Tom Cruise really enjoy his train rides, but she also played a member of Carter's extended family in 1999.
Natalie Portman
Reese Witherspoon
Rebecca De Mornay
After making a name for herself in "Risky Business," Rebecca De Mornay spent five episodes on "ER" as Elaine, the ex-wife of Carter's heroin-addicted cousin Chase. She also managed to have a little fling with Carter, but it wasn't meant to last.
Charlize Theron
Early in his career, this then-unknown actor appeared in a season 7 episode of "ER," playing an injured football player.
Brad Pitt
Denzel Washington
Mel Gibson
Wentworth Miller
His starring role in "Prison Break" was still a few years away when Wentworth Miller showed up in the emergency room. He played a high school football player who was injured not during a game, but during the ensuing riot.
After having a close encounter and revealing herself to be Phoebe Buffay's real mother, this actress, spent a little time in the "ER."
Teri Garr
Teri Garr has had a long career that includes both movies and television appearances. In 1999, she made a guest appearance in the fifth-season episode called "Getting to Know You."
Krysten Ritter
Emilia Clarke
Jessica Chastain
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Later she got "hitched" to Will Smith on the big screen, but when she was just getting started, this Latin beauty had a small role on "ER."
Jessica Alba
Eva Mendes
Eva Mendes had barely begun her career when she appeared in a season four episode of "ER." At that time, she spelled her last name Mendez, so that's how it appears in the credits.
Salma Hayak
Rosie Perez
We loved him as the long-suffering cop who just wants to retire, but this veteran actor also showed up on "ER" as the father of one of the doctors.
Denzel Washington
Morgan Freeman
Forest Whitaker
Danny Glover
In 2005, Danny Glover took a break from the Lethal Weapon franchise to appear in four episodes of ER. He played the long-lost father of Greg Pratt who had abandoned his son years earlier.
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