Usually when you're visiting the doctor, the only thing on your mind is whether or not they can help you get healthy again. You're a little bit nervous perhaps, but definitely not scared.
What's certain is that the last thing on your mind is whether or not he's about to murder you. But the stories of these five doctors might change all that.
We've all seen the movies - from the evil Hannibal Lector in Silence of the Lambs, to the monstrous Dr Heiter in The Human Centipede, but surely they can't exist in real-life... can they?
Scroll down for five of the most evil doctors to ever walk the face of the earth.
1. Beverley Allitt
Location: Lincolnshire, England
Death count: 4
Over fifty-nine dark, disturbing days in 1991, Beverley Allitt murdered four children in the city's local hospital by administering lethal doses of insulin and injecting "air bubbles" into their blood streams.
We'll never know exactly why she did it, but she was later diagnosed with Münchausen syndrome. This controversial psychological condition apparently involves "a pattern of abuse in which a perpetrator ascribes to, or physically falsifies illnesses in someone under their care to attract attention."
She also attempted to murder three other children, and badly injured six more. She was caught and sentenced to thirteen life sentences.
2. Jane Toppan
Location: Boston, Massachusetts
Death count: 31
Jane Toppan was an American nurse who killed at least thirty-one of her patients by administering lethal injections of morphine. Though 31 may be optimistic, it's possible Toppan killed up to 70.
She apparently used her youthful good looks to evade suspicion and is quoted as saying that she wanted to kill more people than anyone who has ever lived before.
She was eventually caught and sent to a mental hospital, where she lived for forty years until her death in 1938.
3. Michael Swango
Location: Illinois, Ohio.
Death count: At least 30.
Swango's patients started dying with poisonous chemicals in their bloodstream whilst he was intern early in his medical career.
To escape suspicion he decided to take a job as an ambulance driver because he admitted that he "liked seeing the blood and gore of accidents".
After poisoning more patients later in his career, Swango slipped out of the country and hid in Europe for several years. When he finally tried to re-enter the United States in 1997, officials were waiting for him at the airport. He was arrested and sentenced to life in prison without parole.
4. John Bodkin Adams
Location: Eastbourne, England
Death count: 100+
Dr. John Bodkin Adams was a British doctor who is strongly suspected of killing over one hundred and sixty of his patients.
The strange thing is that the general practitioner was especially friendly towards his elderly female patients, so much so that often rewrote their entire wills to leave their fortune to him. The patients would pass away shortly afterwards.
He's possibly the most ruthless and heartless of the lot.
5. Harold Shipman
Location: Hyde, England
Death count: 200+
Harold Frederick Shipman was a British doctor and one of the most prolific serial killers in recorded history. On 31 January 2000, a jury found Shipman guilty of 15 murders.
It wasn't until Shipman made a monumentally stupid mistake that he was finally caught. He had killed an older patient and forged a new will, which ignored the victim's family and instead left him with a very large monetary inheritance.
The patient's daughter insisted on an investigation, and when the patient's body was exhumed coroners discovered that she had overdosed on a medical form of heroin.