Zac Efron
Where you know him from: The Greatest Showman, Baywatch + many more memorable shirtless moments.
Made famous by the Disney Channel, this Hollywood heartthrob once played a young man with a fatal gunshot wound. 

Chris Pine
Where you know him from: Star Trek, Wonder Woman + various rom-coms.
Captain Kirk once came into the ER after too many drinks at a Valentine’s Day party. Classic.

Dakota Fanning
Where you know her from: Sweet Home Alabama, The Secret Life of BeesThe Twilight Saga
Hollywood’s golden girl had her first-ever acting role on ER. Just six years old at the time, she played a young girl with leukaemia. 

Shia LaBeouf
Where you know him from: Transformers
Before he was saving the world from robots, Baby LeBeouf was a smart-mouthed young man in a wheelchair. 

Chadwick Boseman
Where you know him from: Black Panther
He might be invincible now, but Boseman was once a humble boxer, who needed a trip to the ER after a rough bout. 

Kristin Davis
Where you know her from: Sex and the City
Known to most women as Charlotte, Davis played a flirtatious patient named Leslie in ER’s first season.

Ewan McGregor
Where you know him from:  Trainspotting, Moulin Rouge, Star Wars  + too many more to name.
One of Hollywood’s most recognisable faces now, in ER Mcgregor played a youth who held people hostage in a convenience store. 

Alexis Bledel
Where you know her from: Gilmore Girls
Known globally as Rory, and more recently as Emily on The Handmaid’s Tale, Bledel appeared in ER’s last ever episode, as a new intern. 

Kirstin Dunst
Where you know her from: Spiderman, Marie Antoinette + others.
Around the time of her big break, Dunst played a young prostitute being rehabilitated by Dr. Ross. 

Lucy Liu
Where you know her from: ElementaryCharlie’s Angels + heaps of other kick-ass kung-fu movies.
Before landing her breakout role in popular sitcom Ally McBeal, Liu played a single mother whose son had AIDS.

Mena Suvari
Where you know her from: American Pie, American Beauty 
The girl next door once played a cheerleader named Laura, on ER in 1996.

Matthew Settle
Where you know him from: Gossip Girl
Attention, Upper East Siders. Before he was Rufus Humphrey, Settle was Abby’s neighbour and an abusive husband. 

Christina Hendricks
Where you know her from: Mad Men
Before she was the vivacious Joan, Hendricks was Joyce, the timid, friendly woman who also lived in Abby’s building.

Stana Katic
Where you know her from: Castle
The famous Kate Beckett once played a patient who was disorientated after waking up from a long coma. 

Josh Radnor
Where you know him from: How I Met Your Mother
More of a comedy man now, in the medical drama Radner played the lover of a councilman who had syphilis. 

Aaron Paul
Where you know him from: Breaking Bad
Paul’s troublesome ER character Doug could be likened to his Emmy-winning Jesse Pinkman, in personality and appearance. 

Octavia Spencer
Where you know her from: Hidden Figures, The Help
Before she was an Oscar-winning physicist, Spencer was a pregnant patient, who faked pains in order to find out if she was carrying a boy or a girl. 

Josh Hutcherson
Where you know him from: The Hunger Games
Before Peeta became a District 12 hero, he was a scared little boy who lost his family to a drunk-driving accident. 

Nick Offerman
Where you know him from: Parks & Recreation
It’s hard to imagine Ron Swanson as anybody but his unapologetic self, but before Parks & Rec, Offerman played a rocker whose bandmate was rushed to the ER.

Adam Scott
Where you know him from: Parks & Recreation
Offerman’s city council colleague was the victim of a car accident in ER’s first-ever episode. 

Eric Stonestreet
Where you know him from: Modern Family
The Emmy-winning actor starred in a 2007 episode of ER, as a Star Trek megafan who tried to Vulcan-ise his own ears.

Ariel Winter
Where you know her from: Modern Family
She made her mark as Alex Dunphy, but the young Winter played Lucy on ER, a girl whose mother needed emergency surgery. 

Jared Padalecki
Where you know him from: Supernatural
In a slightly more realistic world, Padalecki was a teenager who was in a car crash. 

Tobin Bell
Where you know him from: Saw
The master manipulator of your nightmares was once County General’s hospital administrator.

David Schwimmer
Where you know him from: Friends
Schwimmer never actually appeared on the show, but Dr. Gellar was also Dr. Karubian on ER, in an uncredited audio-only cameo. 

Mariska Hargitay
Where you know her from: Law & Order: SVU
A slightly more youthful Olivia Benson was also the front desk clerk at Country General in 1998.

William H. Macy
Where you know him from: Shameless
Macy had a recurring role in ER, in the comparatively respectable position, Chief of Surgery.

Gabrielle Union
Where you know her from:  Bring It On
The antagonist in the biggest cheerleading movie of the decade, Union played an injured high school basketball player in an episode of ER

Don Cheadle
Where you know him from: Ironman, Ocean’s 12
Now an Oscar-nominated actor, Cheadle once played a medical student with Parkinson’s Disease. 

Eva Mendes
Where you know her from: Hitch, Training Day, Ryan Gosling’s baby mama
Mendes’ first acting credit was as a concerned babysitter, who brings her charge into the ER

JK Simmons
Where you know him from: Juno + heaps more
Juno’s doting dad once played Gus Loomer, a man involved in a frightening fatal car crash (it seems there are a lot of those on ER).

Kat Dennings
Where you know her from: 2 Broke Girls, Thor
Dennings has made us laugh for years, with her deadpan portrayal of Max Black. But she once hooked up with ER’s Dr. Barnett, before revealing she was only 14 years old.

The best part? You can see all of these retro cameo performances for yourself, with Seasons 1-5 of ER. Available right here from Wednesday 1 August.