Many patients (played by guest actors) visited the NBC medical drama ER while the TV series was airing in the '90s and the '00s — and many of those actors went on to become household names. It's time for a ranking ER guest stars, because so many celebrities visited County General, and we didn't even know it back then. The list includes actors who would go on to star in Gilmore Girls, Breaking Bad, Gossip Girl, Mad Men, Saw and Wonder Woman. Not bad.
The hit medical drama premiered in 1994 and ran on NBC for 15 seasons until 2009. That's 331 episodes-worth of guest stars who visited the fictional hospital. E.R.'s main original cast included George Clooney (who played Dr. Doug Ross), Anthony Edwards (who played Dr. Mark Greene), Noah Wyle (who played Dr. John Carter), and Julianna Margulies (who played Nurse Carol Hathaway). And the series went on to welcome many new medical professionals over the years, including Angela Bassett (Dr. Catherine Banfield), John Stamos (Dr. Tony Gates), Maura Tierney (Dr. Abby Lockhart), and Kellie Martin (Dr. Lucy Knight).
You may not have known it at the time, but many of the guest-starring patients those main characters treated would go on to become big names themselves. Here are the best guest stars from E.R.'s long history, ranked from awesome to most awesome.
Attention, Upper East Siders: Before Settle played Rufus Humphrey on Gossip Girl, he guest starred on ER in 2002 as Abby's neighbor Brian, who is an abusive husband to Joyce (played by Christina Hendricks).
She would go on to star in American Pie and American Beauty, but Suvari played a cheerleader named Laura in a Season 3 episode of ER that aired in 1996 first.
A few years before she played Charlotte on Sex and the City, Davis played Leslie, a young woman who flirted with Dr. Ross in a first season episode of ER.
Liu landed her breakout role in Ally McBeal later, but in ER she played a single mother named Mei Sun Leow whose son has AIDS.
Before starring on CSI, Eads played a paramedic who expressed romantic interested in Carol Hathaway during a EMT ride-along.
Fans probably know her from Castle, but Katic turned up in a pair of 2005 episode of ER as Blaire, a patient who wakes up from a coma.
The UnREAL actor appeared in the 1994 pilot episode of ER as a pregnant teenager. Years later, Appleby would join the medical drama as intern Dr. Daria Wade in ER's final season in 2009.
Appleby told Elle the following in 2015 about her two roles on ER:
"I was in the pilot of ER, I played a 15-year-old pregnant girl they were treating. And then in the final season they were casting for interns. I had literally just been in the actual E.R. because I broke my pelvis and tailbone and told my agent, 'I really want to be on ER' So then I was in the entire last season of the show. It was amazing. It was like being in graduate school for television. I learned that this is how you do television at the highest level."
Here's how you may have met Radnor before he starred in How I Met Your Mother: the actor played Keith Mitchell, the lover of an alderman who has syphilis.
Before she played Joan in Mad Men, Hendricks guest starred on ER in 2002 as Abby's friendly neighbor Joyce, who is a victim of domestic abuse.
The Oscar-nominated actor played a nun-in-training who suspects that she might be pregnant in a 1995 episode from ER's first season.
Uudiences loved Offerman as Parks & Recreation's Ron Swanson. Years previous, the actor guest-starred as rocker named Rog in the 1997 live episode of ER.
Offerman's former Parks & Rec co-star also guest starred on ER. Scott played David Kerstetter in a 1995 episode from the show's first season.
Scott told TVLine the following about the role: "It was the first season of ER, so it was a pretty big. Everyone was discovering it, and George Clooney was on the cover of TV Guide as this new star. I was sitting outside waiting to work and he was playing basketball with a bunch of dudes. I remember just thinking, ‘God, this dude is on the cover of TV Guide!'"
In 1998, the Emmy-winning Modern Family actor had a recurring role on ER as Roxanne Please, a love interest of Dr. Carter.
The Emmy-winning Modern Family actor guest starred in a Season 7 episode of ER as a Star Trek fan who attempted to Vulcan-ize his ears.
One half of Drake & Josh guest starred on a 2001 episode of ER. Peck played Nick, a teen who needs a third heart transplant.
Before starring in Supernatural and Gilmore Girls, Padalecki appeared on a Season 7 episode of ER as a patient named Paul Harris, who is inolved in a car crash with his dad (played by James Belushi).
Of course, Weil starred as Paris Gellar on Gilmore Girls. She also appeared on ER in several episodes as Samantha Sobriki, the wife of the man who stabbed Dr. Carter and Lucy Knight.
The Gilmore Girls and Handmaid's Tale actor guest starred on the final episode of ER, playing Dr. Julia Wise, a new intern at County General.
Paul is known for his Emmy-winning role as Jesse Pinkman on Breaking Bad. Years before the AMC drama premiered, the actor guest starred on ER's ninth season as a very Jesse-like character named Doug.
The doctors of County General were totally unaware that the future Jigsaw of the Saw movies played a hospital administrator in ER's 1994 pilot episode.
In ER Season 9, The Hunger Games actor played Matt, a young boy whose family is killed by a drunk driver in a 2002 episode.
The Friends actor made an uncredited audio-only cameo in a 1996 episode of ER as Dr. Karubian, a surgeon called by Dr. Carter.
Law & Order: SVU's Hargitay played ER front desk clerk Cynthia Hooper throughout ER's Season 4 in 1998. She and Dr. Greene have an imbalanced relationship that ends with him breaking up with her in California.
16Taraji P. Henson
In a 2000 episode of ER, LaBeouf played Darnel Smith, a smart-mouthed young man in a wheelchair who has muscular dystrophy.
The late Star Trek actor appeared on ER at nine years old in a Season 6 episode that aired in 2000. Yelchin played Robbie Edelstein, a young boy whose parents both die in a car accident.
The Trainspotting actor guest starred as Duncan Stewart, who holds a group of people hostage (including Carol) during a convenience store robbery in Season 3.
In August 2017, McGregor remembered the ER episode in an interview with The Hollywood Reporter:
"I loved making it, and I loved working with Julianna Margulies a lot because I was a big fan of that show, and I asked to be on it. I told my agent to see if I could be on it because I was a big ER fan. And I loved her. I love her work. So I remember I mainly worked with her, and it was like a special one hour. It was all shot in Chicago. I enjoyed it."
12William H. Macy
The Shameless actor appeared on ER in the recurring role of Dr. David Morganstern, County General's Chief of Surgery and Emergency Medicine. He appeared throughout ER's first four seasons, as well as an episode in 2009.
The actor played an injured high school basketball player named Tamara in a 2000 episode in ER's Season 6.
After her breakout role in the 1994 film Interview with a Vampire, Dunst had recurring role on ER Season 3 as Charlie, a young prostitute being rehabilitated by Dr. Ross.
The Oscar-nominated actor played medical student Paul Nathan in a few 2002 episodes of ER's ninth season. Nathan had Parkinson's Disease.
Before giving us chills in Get Out, Whitford played Sean, a young dad-to-be accompanying his pregnant wife to the hospital in a devastating Season 1 episode.
The Ocean's 8 actor's first big role was playing Delia Chadsey, a young girl who is taken to the ER after a car accident and finds out her leukemia has returned. Fanning was just 6 years old at the time.
Get this — Mendes' very first IMDb credit is her guest-starring role on ER in 1998. The actor plays a concerned babysitter named Donna, who brings in a young girl she was caring for.
The Oscar-winning actor guest starred on ER Season 10 in 2004. Simmons played Gus Loomer, a man who is involved in a fatal car wreck.
The Oscar-nominated actor appeared in ER Season 10 in 2004, in which she plays a daughter accompanying her father to County General. It is Chastain's first acting credit, according to IMDb.
The Oscar-winning actor once made an appearance on an ER Season 5 episode, in which she played a woman named Maria who fake pains in order to find out if she was pregnant with a boy or a girl.
Yup, you read that right. Efron rolled up to the doors of County General in a 2003 episode as Bobby Neville, a young man with a fatal gunshot wound.
The Wonder Woman actor got his first credited role as a guest star on the NBC medical drama. In a 2003 episode, Pine played Levine, who visits the ER after drinking too much at a Valentine's Day party. This is Pine's first IMDb credit, according to an IMDb interview with the actor. "I remember on the stage they built and the entire ER was unbelievable," he told IMDb in the video interview. "It was my first time doing anything scripted and long, and it was really neat."
Can you believe so many amazing actors visited ER as patients and guest stars? It'll make you want to revisit the series and pay some more attention to the guest cast that comes through.