57 guest stars you might have forgotten were on 'Grey's Anatomy'

Moss played a character named Nina Rogerson in episode 19 of season three. Nina's mother is a hospital patient in need of a risky surgery.

She played Ruby, a young girl who saves her mother's life. After her mom gets injured, she calls the hospital, and the doctors walk her through a life-saving procedure. She then spends time applying CPR until a helicopter arrives and rescues them both.

Moore played Mary Portman. She's first introduced in the two-part season six finale. She's in the hospital for a colostomy bag reversal surgery when the hospital is shut down because of an active shooter. She and her husband decide to travel and return to the hospital for the surgery six months later. She ends up in a coma after her surgery and her husband takes her off of life support.

A surgical intern at the other hospital in Seattle, Marshall caused a car accident involving three cars. He didn't suffer any critical injuries, but one victim died.

Lovato played a girl named Hayley May in episode 22. May is incorrectly diagnosed and almost placed in a psychiatric ward, but is later correctly diagnosed and undergoes a successful surgery.

Paulson played a young Ellis Grey. The flashback shows her and a young Richard Webber caring for their first patient diagnosed with GRID, later known as AIDS.

Palmer played a young girl named Sheryll Jeffries. She arrives at the hospital pregnant, hoping to take part in Christina Yang's trial since she needs a heart transplant. Christina denies giving her a spot in the trial because of her age. She gives birth prematurely.

Chung played Trina Paiz, a newlywed who falls 100 feet into a ravine during her honeymoon. Both she and her critically injured husband survive.

Ultimately, neither Alana nor the doctors could save the hospital. Catherine Avery stepped in and had the Harper Avery foundation invest in the hospital.

She sticks her hand inside a patient's wound to prevent bleeding, but learns that she may be keeping bomb ammunition in place. So she has to leave her hand in it or risk it exploding.

As Dylan carries the bomb to a safe location, it explodes and kills him. Chandler returns for season three during Meredith Grey's "afterlife" visions during her near-death experience.

The night of her prom, Camille passes out during sex. And while at the hospital, she learns her ovarian cancer has returned. She was replaced by Camille Winbush on season four.

Because Megan can't feel pain, she doesn't know when her injuries are bad. She had a kid hit her in the stomach with a baseball bat 25 times, so she was suffering from internal injuries. When the doctors discover this, they take her into surgery.

Kyle is a musician diagnosed with multiple sclerosis. He starts a relationship with resident Stephanie Edwards. He later succumbs to an infection.

Liz flies to Seattle to donate a nerve to help fix her brother's hand.

Morgan first shows up on season two as a patient in need of a heart transplant. He eventually becomes Izzie's love interest and the two form a relationship. She cuts his LVAD wire, so he can get a heart transplant. And though the surgery is successful, he dies from a stroke later that night. He returns posthumously on seasons three and five during Meredith's near-death experience and during Izzie's hallucinations brought on by her brain tumor.

She arrives to help with a pediatric surgery case. While in Seattle, she has a one-night stand with Arizona Robbins.

Smollett played Beth Monroe, a young girl suffering from an inoperable tumor. She arrives with her boyfriend, suffering from the same tumor, to participate in Meredith Grey and Derek Shepard's trial. She survives, but her boyfriend doesn't.

Her character, Karen, needs to receive the transplant from her sister Marcy, but the two constantly bicker before and after the surgery.

Meredith dates both Finn and Derek Shepard to see who she cares for more. But while she likes Finn, she loves Derek.

Odom appeared on episode five. His character, P.J. Walling, becomes part of a domino kidney transplant after his dad, who needs a kidney, offers him $10,000 to do it.

His wife finds out he is having an affair prior to the surgery.

Lowes played a blood donor on episode 22 of season seven.

Henry is first introduced as a patient denied surgery at the hospital because he doesn't have insurance. One doctor, Teddy Altman, proposes marriage to save his life. The two form a relationship, but the end is ultimately heartbreaking.

Young portrayed Kathy, a woman who returns multiple times to the hospital with various injuries. She reveals that she turns to exercise to avoid cheating on her husband because they haven't had sex in more than a year. After tests, they discover that he has a tumor.

He has a complicated relationship with Meredith after divorcing her mother, Ellis. The two eventually bond, but it's not easy after the death of his second wife at the hospital and his alcoholism.

As Alison Clark, she befriends Izzie during rounds of chemotherapy. She never wakes up after her surgery and dies.

He played Seth Hammer, the husband of a hypochondriac patient.

She initially came in for a kidney stone removal, but Derek Shepard says he can fix her spine. She is able to receive the surgery after an anonymous donor steps in to cover the cost since her insurance won't.

He played Ryan, a young boy born with no external ears, but he still has the ability to hear.

She played a pregnant woman who is trapped and injured with her fiancé when a tunnel collapses as they go to the hospital. They both survive and she gives birth to a son.

A very affluent man, Carlos tries to exert his influence over his daughter and briefly cuts her off from the family after arguing over her life. He eventually accepts her again and is present for her wedding to Arizona.

Casey doesn't give up on her son and he is finally diagnosed.

After a testy initial relationship, he becomes Christina Yang's mentor and the two work together on surgeries.

She played Donna, a transgender patient diagnosed with breast cancer while transitioning from male to female.

Green's character, named Nick Hanscom, is a patient who has an exposed carotid artery after a tumor resection. It eventually bursts, but he dies as the doctors try to repair the artery.

Her character, Kim Dawson, is introduced as a marriage counselor for Arizona Robbins and Callie Torres. The couple ultimately splits after their therapy.

Sarabeth is with a group of her girlfriends on the way to a ball when their limo gets in a car wreck. She drives the limo to the hospital after the driver is injured.

As an older intern, he is mistaken for a resident. He eventually switches from surgical to psychiatry.

She trains Arizona Robbins, but must have surgery for brain tumor. The surgery results in her going blind.

Stan and his ambulance partner are about to leave the hospital when another ambulance crashes into them, flips their truck, and traps them. Stan's legs are trapped so that when they go to rescue his partner, he will bleed out and die. His wife works in the hospital, so the doctors get her for an emotional goodbye.

Her character, Gayle McColl, is the estranged wife of a patient at the hospital on episode 14. She arrives at her estranged husband's bedside and reveals the other woman as his girlfriend. When he husband wakes up from his surgery with memory loss, the two reconnect, and she remembers how much she loves him. Unfortunately, he dies in a second surgery.

He played a man whose husband dies from injuries sustained in a car accident. He doesn't want to pull the life support, but he does.

He finds out about Jo's fake name and surprises her at Grey Sloan. He introduced her to his fiancée, Jenny, and asks Jo to sign divorce papers. Jo tries to help Jenny, but she initially denies any assistance. Paul is later the victim of a hit-and-run.

She initially denies Paul's abusive behavior, but she later decides to go to the police with information.

He wasn't the person Meredith was supposed to be meeting on her blind date, but the two hit it off until he said he didn't like kids. Meredith ended it.

She was in the Army and presumed dead after missing for 10 years but was found and rescued. She wanted to return to her adopted son overseas but needed to recover in the states. Megan was previously engaged to Nathan, and the two reunited when she we recovered. They moved to California with her adopted son.

The doctor himself had recently had a kidney transplant and collapsed in the hospital. He flirted with Meredith while they waited for his lab reports.

Milano reunited with her "Charmed" costar Holly Marie Combs for an episode of the medical drama, which saw Milano and Combs play sisters facing a difficult decision.

"Grey's Anatomy" showrunner Krista Vernoff, who also worked on seasons 3-6 of "Charmed," told People that Combs' and Milano's roles on the medical drama were supposed to reference their previous characters, the Halliwells.

"Our goal was to wink at 'Charmed' while still making an episode of 'Grey's Anatomy,'" Vernoff said.

A young Jesse Plemons is nearly unrecognizable on season two, episode 18. The "Fargo" and "Friday Night Lights" star played Jake Burton, a patient who had a condition that caused bony tumors to grow on and disfigure his face. The tumors also began encroaching on his brain — he died during surgery.

"Dirty Dancing" star Jennifer Grey played Betty's (Peyton Kennedy) mother Carol Dickinson in three episodes of season 15. Betty, whose real name was Brittany, was the troubled teenager who Owen (Kevin McKidd) adopted his son Leo from. Amelia (Caterina Scorsone) was attempting to help Betty get clean.

Grey Sloan doctors thought Zola star Taylour Paige's character Emma was a drug addict who visited the clinic to sober up on her season 13 episode. They eventually discovered she had Ehlers-Danlos syndrome, which is a group of disorders that's very hard to diagnose.

"Pitch Perfect" star Skylar Astin played Todd Eames on four episodes of "Grey's Anatomy." He originally went to Grey Sloan because his sister was having surgery. He became interested in her doctor, Jo Wilson. The pair dated for a short time, but it didn't work out.

"Bonnie & Clyde" star Faye Dunaway played Dr. Margaret Campbell on the 16th episode of season five. Dr. Campbell was an older woman who was set in her antiquated surgical ways. Dr. Cristina Yang (Sandra Oh) thought she should retire.

On season three episode five, "One Day at A Time" star Justina Machado played Anna Nyles.

Anna was a mother with breast cancer who is so exhausted and depressed she's hesitant to treat the cancer until a talk with Dr. Bailey (Chandra Wilson).

On a season six episode, "Roseanne" and "The Conners" star Sara Gilbert played a terminally ill patient named Kim Allen. Kim was at the hospital to die via physician-assisted suicide.