From Lostpedia

Boone is operated on by Jack. ("Do No Harm")

Surgery is a common theme on Lost, and has been utilized both on the Island and off. Most of the surgeries seen on the show were conducted by Jack, Juliet, or Christian, three characters who are best known as doctors. Also, most surgeries are used to significantly advance the plot (i.e. Jack holding Ben hostage to allow Kate and Sawyer to escape).

Season One

• Jack tells Kate the "counting to five" story, about how a surgery on a girl which taught him a valuable lesson about fear.("Pilot, Part 1")
• Kate stitches up Jack's wounds. ("Pilot, Part 1")
• Jack removes the shrapnel from Edward Mars, who later dies. ("Pilot, Part 2")
• Christian Shephard remarks to a young Jack that there was a girl who he did surgery on, who died. ("House of the Rising Sun")
• After Sayid stabbed Sawyer, hitting an artery, Jack successfully stitches Sawyer up. ("Confidence Man")
• Christian Shephard attempts to operate on a pregnant woman unsuccessfully, and despite Jack's best efforts, she dies. This causes Christian to be dismissed from the hospital. ("All the Best Cowboys Have Daddy Issues")
• Locke gives a kidney to Anthony Cooper. ("Deus Ex Machina")
• Jack attempted to heal Boone, even to the point of attempting a blood transfusion, and trying to amputate Boone's leg. However, Boone died. ("Do No Harm")
• Locke references the surgery game Operation when removing dynamite from the Black Rock. ("Exodus, Part 2")

Season Two

Sarah after being healed. ("Man of Science, Man of Faith")

Jack operates on Ben, while Sayid and Locke look on. ("One of Them")

• Jack operates of Sarah Shephard, the victim of a car accident, attempting to fix her paralysis. Miraculously, the surgery works. ("Man of Science, Man of Faith")
• Jack operates on Angelo Busoni's spinal tumor, unsuccessfully. ("The Hunting Party")
• Jack worked to heal Sawyer, who had been shot by Tom. ("What Kate Did")
• Jack had to remove the arrow from Ben's shoulder. ("One of Them")
• Jack attempts to save Libby, who had been shot by Michael. Eventually, she dies. ("?")

Season Three

Ben on the operating table ("I Do")

• Jack does surgery on Colleen in an unsuccessful attempt to save her. ("Every Man for Himself")
• Jack performs surgery on Ben to remove his spinal tumor. He then holds him prisoner until Sawyer and Kate can escape. ("I Do") ("Not in Portland")
• Sabine died on Juliet and Ethan's operating table. ("One of Us")

Season Four

Jack's surgery. ("Something Nice Back Home")

• Juliet loses Henrietta during surgery. ("The Other Woman")
• Juliet performs an appendectomy on Jack. ("Something Nice Back Home")

Season Five

Juliet tries to save Ben ("Whatever Happened, Happened")

• Hajer hurriedly re-sets Locke's broken leg after he arrives in Tunisia. ("The Life and Death of Jeremy Bentham")
• Juliet and Debra attempt to fix Ben after he was shot by Sayid. ("Whatever Happened, Happened").
• Jack is seen performing his first solo surgery when he accidentally cuts the patient's dural sack. ("The Incident, Parts 1 & 2")