Heaven Canceller (A Certain Magical Index) can heal anything, whether it is terminal illness or mortal wounds, distorting the laws of heaven, so long as the patient is still alive.
Fiona Fox (Archie's Sonic the Hedgehog), is knowledgeable in medicals.
Doctor (Black Cat) is very skilled in medicals, using soft chi kung to accelerate cellular functions, healing wounds and reattaching limbs.
Retsu Unohana (Bleach) is considered the best healer in Soul Society.
Mayuri Kurotsuchi (Bleach) is very knowledgeable in medical science, having modified many people, including himself, in very innovative, yet disturbing, ways.
Szayelaporro Granz (Bleach) uses his scientific expertise to modify many of his subordinates for extra strength, or transform them into walking medicament.
Tenjirō Kirinji (Bleach) is the most powerful known healer, having taught Unohana many of her medical skills, personally he specializes in balneotherapy, having invented powerful healing hot springs that not only cleanses bodies of impurities...
...but also instantly replenished lost blood.
Kanzaki Keine (Choujin Koukousei-tachi wa Isekai demo Yoyuu de Ikinuku you desu!) is a medical prodigy and the finest doctor in the world, having successfully saved thousands of patients without a single death.
Although psychotic and completely deranged, Professor Pyg (DC Comics) is an adept surgeon who can perform complicated surgeries.
Alfred Pennyworth (DC Comics) can perform first aid and more complex medical procedures such as arthroscopy and other advanced surgery to suture grievous wounds and remove bullets, limiting the need for hospital care for the Batman Family.
A world-class surgeon and neurologist, Tommy Eliot/Hush (DC Comics) has achieved extraordinary, near-impossible medical breakthroughs with his talents alone...
...most infamously feat is surgically stitched a collection of certain facial features from inmates in Arkham City to his own face to look exactly like Bruce Wayne.
Ra's al Ghul (DC Comics) was a genius master physician, whose medical knowledge was six hundred years ahead of his contemporaries. He even managed to refine the Lazarus Pit to bestow immortality and regeneration.
Dr. John Zoidberg (Futurama) was considered by Professor Farnsworth to be a fine physician for aliens despite his knowledge for human physiology being absolutely atrocious.
As the divine physician of Olympus, Apollo (Greek Mythology) is the Greek God of Medicine and Healing, not only can he give divine protection from epidemics but also induced deadly plague via his arrows.
Apollo's disciple, Chiron (Greek Mythology) is legendary as the founder of Greek herbalism and pharmacy.
The demi-god physician, Asclepius (Greek Mythology) has surpassed his father Apollo and mentor Chiron in the art of medicine, able to even heal others back to life from the brink of death and beyond.
Dr. Gregory House (House) is well-known for his excellent, if unorthodox, methods of practicing medicine.
Stephen Strange (Marvel Cinematic Universe) was one of the world's most renowned neurosurgeons.
Tsunade (Naruto) is heralded as the Greatest Medical Ninja in History, able to perform even the most complicated surgeries and even developed the ultimate regeneration technique.
Orochimaru (Naruto) has tremendous knowledge on the human body, having studied so long to achieve immortality and drawing out human strength.
As Tsunade's first disciple Shizune (Naruto) is one of Konoha's finest masters of medical ninjutsu...
...able to successfully perform the most difficult surgical ninjutsu such as Healing Resuscitation Regeneration technique to save a mortally wounded Neji.
Kabuto Yakushi (Naruto) is a very powerful medical ninja, so full of surprising talent that even Tsunade believes him to surpass her prime.
Sakura Haruno (Naruto) has inherited all of Tsunade's medical skills, being her second disciple, and is considered to be her equal in prime.
Obito Uchiha (Naruto) possesses such skill in surgery that he was able to transplant one of Madara Uchiha's Rinnegan into himself.
Chiyo (Naruto) was considered to be one of the best medical ninjas in Hidden Sand Village/Sunagakure, as she created many poisons, and can even transfer life force to bring the dead back to life and heal the injured.
Shinnō (Naruto) may have utter disregard for human life, but his immense knowledge in the human body allows him to perform flawless surgeries with only minor tools, and even enhance his own body.
Haku (Naruto) is knowledgeable herbalist and also a master of acupuncture...
...using his Thousand Needles of Death to precisely strike all his enemies's pressure points to kill them.
Trafalgar D. Water Law (One Piece) is a genius surgeon, he can treat the most brutal injuries such as magma burns, and with his Ope Ope no Mi, he can perform miraculous surgeries to treat incurable diseases.
Caesar Clown (One Piece) has tremendous medical knowledge, as he could use his chemical expertise to apply healing and turn children into giants, as well as create artificial Devil Fruit ingredients that affect the bloodline.
Doctor Kureha (One Piece) is one of the finest doctors in the world. She could maintain her aging 141 year old body in top physical health and condition and trained Chopper into an outstanding medic.
A brilliant student of Kureha, Tony Tony Chopper (One Piece) is extraordinarily multi-talented prodigy in all fields of medical science...
...even inventing a drug to enhance his Devil Fruit.
The Torino Tribe (One Piece) are the world's foremost masters of herbalism and pharmacology,...
...having researched and developed a massive collection of powerful medicines, far more advanced than most countries.
Rebecca Chambers (Resident Evil) possesses extensive knowledge in medical science.
Johann Faust VIII (Shaman King) has extraordinary talent in medical science. He could cure Eliza of an incurable disease, and came up with unorthodox and gruesome, but effective healing methods such as deboning fractured bones to replace it with bones from corpses.
A surgical genius, Cioccolata's (JoJo’s Bizarre Adventure Part V/5: Golden Wind/Vento Aureo) sick medical experiments on his patients gave him an intimate knowledge of the human body, especially which body parts he can cut while preserving his victim's life...
...and with his surgery skills, he could perform surgery on himself quickly enough to bisect and reattach his own body.
Dr. Mario (Super Mario) is an excellent physician, having created special Megavitamins that can cure the common cold and the flu.
Asclepius (Valkyrie Crusade)
Minoru Kamiya (Yu Yu Hakusho) has medical knowledge as knowing the by striking certain pressure points/joints.