(Covers information from Both Timelines)
In 2001, Adam Rutherford, and Sarah were taken to St. Sebastian after their accident. Jack Shephard chose to save Sarah over Adam, as Adam's case was hopeless. Adam was pronounced dead at 8:15 am. Jack's father, Christian Shephard, was Chief of Surgery at that time. ("Man of Science, Man of Faith") Adam's daughter, Shannon Rutherford, and his wife and Shannon's stepmother, Sabrina Carlyle, later met at the hospital after having learned about Adam's death. ("Abandoned") A short time later, Jack operated on Sarah and miraculously restored her ability to walk. ("Man of Science, Man of Faith")
Several years later, Angelo Busoni, who had an inoperable spinal tumor, chose St. Sebastian for his operation. He specifically asked to be operated on by Jack. His daughter, Gabriela Busoni, accompanied him. Even though the situation was hopeless, Jack decided to operate anyway, but Angelo died on the operating table. ("The Hunting Party")
In July 2004, Christian Shephard (who was a longtime alcoholic) fatally botched a surgery on a woman named Beth while under the influence. Even though he attempted to get Jack to help him cover it up, Jack reported his father, which resulted in Christian losing his position at St. Sebastian. ("All the Best Cowboys Have Daddy Issues")
Following his return from the Island, Jack continued to work at St. Sebastian. In early September 2007, he was preparing for a surgery on a patient named Ms. Berenberg when he started seeing his dead father. ("Something Nice Back Home") This eventually caused him to start drinking and becoming addicted to pills. After having saved a woman, Mrs. Arlen, from a burning car wreckage (who had in fact crashed her car when she saw Jack trying to commit suicide), Jack insisted on operating on her, but the new Chief of Surgery at St. Sebastian, Dr. Hamill, relieved Jack of his duties, realizing his heavy substance abuse. ("Through the Looking Glass, Part 2")
A few days later, David Reyes brought a heavily tranquilized Sayid Jarrah to Jack, who in turn brought Sayid to St. Sebastian. Despite being suspended from work, Jack successfully treated Sayid, causing him to wake up. ("The Lie") Shortly after, the Chief of Clinical Services, Evelyn Ariza, called Jack and reminded him that he had been suspended from work. In the meantime, an operative of an unknown force disguised as a male nurse attempted to sedate Sayid again, but was successfully overpowered by Sayid just as Jack and Ben Linus entered Sayid's hospital room. Subsequently, the three left St. Sebastian. ("The Little Prince")
Omer Jarrah is brought to St. Sebastian after being badly beaten. Jack Shephard is seen briefly in a hallway. Another doctor tells Nadia and Sayid that Omer was mugged and suffered a punctured lung. ("Sundown")
St. Sebastian Hospital; this lobby exterior is the same set location as the Lynford Hotel
St. Sebastian appears to be within driving distance of the stadium where Jack and Desmond first met, since Jack goes there to run the steps after his frustration with Sarah's surgery. ("Man of Science, Man of Faith")
- Christian Shephard - Former Chief of Surgery
- Jack Shephard - Spinal Surgeon
- Unnamed head doctor - chaired the committee looking into the death of Beth and the actions of the Shephards.
- Dr. Hamill - Present Chief of Surgery.
- Andrea - intern
- Unnamed anesthesiologist - present at Christian and Jack's surgery on Beth.
- Unnamed anesthesiologist - present at Jack's emergency surgery on Adam Rutherford.
- Unnamed anesthesiologist - present at Jack's "Count to five" surgery.
- Unnamed doctor - told Shannon and Sabrina about the death of Adam Rutherford.
- Brian Costas - intern, present at the arrival of Adam Rutherford, told Jack he couldn't intubate. Called time of death on Adam Rutherford.
- Unnamed nurse - worked with Jack and took care of Locke
- Unnamed doctor - treated Jack for injuries sustained while rescuing a woman and her son from a crashed car (post-island).
- Dr. Leon is mentioned over a tannoy in "Through the Looking Glass, Part 1".
- Gary Nadler is mentioned by Dr. Hamill in "Through the Looking Glass, Part 1".
- Jane - Jack's secretary. ("Something Nice Back Home")
- Unnamed receptionist - receptionist. ("Something Nice Back Home")
- The St. Sebastian Neurosurgery Group as cited in "Something Nice Back Home":
- Evelyn Ariza - administrator ("The Little Prince")
- Buchanan (EMT No. 1) ("Man of Science, Man of Faith")
- Unnamed EMT ("Man of Science, Man of Faith")
- Jack Shephard - spinal Surgeon
- Juliet Carlson - OB-GYN
- Unnamed doctor - in the flash-sideways timeline, unnamed doctor who tells Nadia and Sayid about Omer's condition ("Sundown")
- Unnamed doctor
- Unnamed nurse
- Nurse Tyra
- Unnamed MRI tech
- Simon Holt - EMT ("The Last Recruit")
- Lynn Johnson - EMT ("The Last Recruit")
- Unnamed surgeon
- Unnamed orderly
- Jean - nurse
- Unnamed receptionist - receptionist. ("The Substitute")
- According to legend, St. Sebastian was martyred by being tied to a tree or post and shot with arrows (the arrow being his attribute). He is the patron saint of soldiers and youth, among other things. He is also a protector from the plague. (Through the Looking Glass-Enhanced transcript)
- The filming location is the St. Francis Medical Center in the Liliha district of Honolulu. 
- The exterior driveway entrance is the same location as used for the Lynford Hotel front lobby entrance in "A Tale of Two Cities".  Compare with this image.