| Actor/actress | Character | Role |
|---|---|---|
| Anthony Edwards | Dr. Mark Greene | ER/EM Chief Resident |
| George Clooney | Dr. Doug Ross | PGY-4 Emergency Paediatric Resident |
| Sherry Stringfield | Dr. Susan Lewis | ER Junior Resident (Year 2) |
| Noah Wyle | John Carter | Rotating Medical Student Year 3 |
| Julianna Margulies | Nurse Carol Hathaway | ER Nurse |
| Eriq La Salle | Dr. Peter Benton | Surgical Resident (Year 2 GS) |
- Doctors and Medical students
- William H. Macy as Dr. David Morgenstern – Chief of Surgery and Emergency Medicine
- Sam Anderson as Dr. Jack Kayson – Chief of Cardiology
- Amy Aquino as Dr. Janet Coburn – Chief of Obstetrics and Gynecology
- CCH Pounder as Dr. Angela Hicks – Surgical/Emergency Medical Attending Physician
- Ming-Na Wen as Deb Chen – Third-year Medical Student
- Michael Ironside as Dr. William "Wild Willy" Swift – Chief of Emergency Medicine
- Scott Jaeck as Dr. Steven Flint – Chief of Radiology
- Rick Rossovich as Dr. John "Tag" Taglieri – Orthopedist
- John Terry as Dr. David "Div" Cvetic – Psychiatrist
- Tyra Ferrell as Dr. Sarah Langworthy – Third Year Surgical Resident
- Perry Anzilotti as Dr. Ed – Anesthesiologist
- Tobin Bell as Dr. Wertz – Hospital Administrator
- Patrick Collins as Dr. Netzley
- Marion Yue as Dr. Sandra Li
- Matt Gottlieb as Dr. Ashley
- Pierre Epstein as Dr. Alex Bradley - Chief of Staff
- Nurses
- Ellen Crawford as Nurse Lydia Wright
- Conni Marie Brazelton as Nurse Conni Oligario
- Deezer D as Nurse Malik McGrath
- Laura Ceron as Nurse Chuny Marquez
- Yvette Freeman as Nurse Haleh Adams
- Lily Mariye as Nurse Lily Jarvik
- Vanessa Marquez as Nurse Wendy Goldman
- Dinah Lenney as Nurse Shirley
- Suzanne Carney as OR Nurse Janet
- Staff, Paramedics and Officers
- Gloria Reuben as Physical Therapist Jeanie Boulet
- Abraham Benrubi as Desk Clerk Jerry Markovic
- Glenn Plummer as Desk Clerk Timmy Rawlins
- Rolando Molina as Desk Clerk Rolando
- Małgorzata Gebel as ER aide (Dr.) Bogdanilivestsky "Bob" Romansky
- Lisa Zane as Risk Management Diane Leeds
- Christine Healy as Hospital Administrator Harriet Spooner
- Emily Wagner as Paramedic Doris Pickman
- Montae Russell as Paramedic Dwight Zadro
- Lee R. Sellers as Chopper EMT
- Mike Genovese as Officer Al Grabarsky
- Rick Marzan as Camacho
- Family
- Christine Harnos as Jennifer "Jenn" Greene
- Yvonne Zima as Rachel Greene
- Georgiana Tarjan as Helen Hathaway
- Khandi Alexander as Jackie Robbins
- Ving Rhames as Walter Robbins
- Beah Richards as Mae Benton
- Tamala Jones as Joanie Robbins
- Mark Dakota Robinson as Steven Robbins
- Kathleen Wilhoite as Chloe Lewis
- Valerie Perrine as Cookie Lewis
- Zachary Browne as Jake Leeds
- Wolfgang Bodison as Al Boulet
Notable guest stars[edit][]
- Andrea Parker as Linda Ferrell
- Miguel Ferrer as Mr. Parker
- Troy Evans as Officer Frank Martin
- Liz Vassey as Liz
- John Randolph as Mr. Franks
- John La Motta as Ivan Gregor
- Rosemary Clooney as Madam X/Mary Cavanaugh
- Alan Rosenberg as Samuel Gasner
- Vondie Curtis-Hall as Henry Colton/Rena
- Jessica Tandy as Mrs. Plecker
- Bobcat Goldthwait as Mr. Conally (voice only)
- Robert Carradine as John Koch
- Bradley Whitford as Sean O'Brien
- Colleen Flynn as Jodi O'Brien
- Kristin Davis as Leslie
- Garrett Morris as Edgar Luck
- Kevin Michael Richardson as Patrick