Natasha Marco is young and fit. The 28-year old aspiring Toronto actress enjoys yoga. She works to keep her body limber and healthy. To do that, she relies on her chiropractor.

"About a year or more ago, I had some sort of back muscle spasm where I couldn't move my neck or my back and I went there. And it completely helped me out, completely, completely helped me."

Marco has been going to the chiropractor since she was a teenager. Like millions of Canadians she believes keeping your spine and neck adjusted improves your health and eases those aches and pains.

Diane Rodrigue was also fit and healthy when she went to a chiropractor seeking relief from neck pain and headaches. But on her last visit, the chiropractor manipulated her neck, and changed her life forever.

"I was able to get up and go back to the desk. Shortly after I felt, I could feel something was wrong so I went back to the office and lay down on the couch and that's when my limbs started to stop moving."

She was just 30 years old, yet Rodrigue had a massive stroke right in the chiropractor's office. It left her completely paralyzed. The chiropractor never accepted blame, but in a settlement agreed to pay her a million dollars eight years ago.

The woman who loved to fish and be outdoors now depends on machines to breathe and caregivers to feed and bathe her. For years, she couldn't speak.

Now through a mechanical device Diane has her voice back.

"I believe chiropractic neck manipulation is very dangerous and should not be done."

The question of just how dangerous it is has erupted into a bitter, public war of words in this country.

It's a battle for the minds and necks of Canadians. The chiropractors say the neck manipulation is safe and they've been doing it for 100 years. But medical doctors claim the evidence is mounting that the risk is far greater than patients have been led to believe.

Chiropractor Deborah Kopansky-Giles teaches at Canada's Memorial Chiropractic College in Toronto. She demonstrates the neck adjustment at the heart of the controversy on Gary Graham, who has been her patient for about 10 years.

Kopansky-Giles checks each of the seven vertebrae in Graham's neck to see which ones need adjustment.

During the manipulation, Graham's neck is extended then quickly rotated.

"I heard a slight crack, but it's nothing I find dramatic or shocking it gives me a bit of relief," says Graham.

Sometimes, as with Graham's manipulation, you hear nothing more than a soft popping sound when the joints move. But every patient and every practitioner is different. Some manipulations appear to use more force and velocity.

Regardless of the method, it's a maneuver some medical doctors say can damage the arteries in the neck. Edmonton neurologist, Dr. Brad Stewart believes it is too dangerous.

"To be frank, it's become clear since I started my neurology residence and have gone into private practice that the risks of neck manipulation, cervical manipulation are highly under-reported. It would not be a week that would go by when I wouldn't see someone with some type of complication following manipulation."

Most strokes happen when a clot breaks off from the heart and moves up to the top of the brain. But a stroke linked to a neck manipulation usually happens at the back of the neck.

There are two thin vertebral arteries that feed blood to the brain. They're most vulnerable right at the top where they bend against the bone. The arteries can tear releasing a blood clot into the brain stem.

The blood clot can then block blood flow and cause a stroke. This can happen accidentally with a sudden twist of the head and it can happen during a neck adjustment.

But chiropractors say the chance of this happening in their hands is virtually nil, according to Canadian Chiropractic Association spokesperson, Stan Gorchynski.

"Chiropractic care, like any other health care intervention, has benefits and risk. The risk is very minimal. We currently have it pegged at about one in a million neck adjustments... That is very acceptable in terms of any health care intervention in Canada or the world."

However neurologists dispute the chiropractors odds of one in a million treatments.

Dr. John Norris is head of the Canadian Stroke Consortium. It's been collecting data gathered from neurologists across the country who believe the benefits are not worth the risk.

"Most patients who go for headaches have to ask if it helps their headache is it worth the risk of being disabled or even killed even if it's one in 100,000."

But the chiropractors challenge the scientific validity of the stroke consortium's data.

"We are on very solid scientific ground for what we are telling patients," says Gorchynski.

A study published last year in the Canadian Medical Association Journal found the risk of stroke even higher for young people under 45 somewhere between one in 5,000 and one in 50,000.

The scientists admit they can't calculate the true risk without more research.

So, is it one stroke in 5,000, one in 100,000 or one in a million? Whatever the risk, Les Limage says it's not worth it.

The Kitchener, Ontario man ended up in intensive care on a respirator with a stroke, five days after visiting a chiropractor.

Until his stroke, Limage had been a healthy active 66-year old. His doctors say he had none of the risk factors for stroke at his age.

Florence Limage will never forget the day last November when she picked her husband up after his appointment at the chiropractor. Les was getting treatment for a sore hip.

"He opened the car door and he said, he cracked my neck. And I said why? He said I don't know. And I said, did you ask him to crack your neck and he said, no."

That weekend Limage developed headaches, a sore neck, double vision, and nausea. The couple never connected the symptoms with the chiropractic visit.

But it's what neurologist Dr. Dwight Stewart suspected when Les had a stroke five days after that neck adjustment.

The tests confirmed a torn artery in the neck, which Dr. Stewart believes was caused by the neck manipulation.

"That's certainly the conclusion one is inevitably drawn toward."

The Limage family is now suing the chiropractor. Limage says he didn't ask to have his neck manipulated and no one warned him about the risk of stroke.

Neurologists claim they see far too many strokes, which they believe are linked to neck manipulations.

"We say the public needs to know. They are not being given the correct information," says Dr. Dwight Stewart.

The chiropractors are angry. They feel their reputation and their livelihood are being unfairly attacked because medical treatments and drugs also have serious side effects.

The medical doctors accuse the chiropractors of twisting and tearing too many arteries. The chiropractors accuse the neurologists of twisting the truth.

But the Canadian Chiropractic Association insists patients should be informed and that chiropractors are telling patients about the signs and symptoms of stroke.

However patients haven't always been informed. In 1986, the editor of the Chiropractic Report was warning chiropractors not to use the "red flag word stroke," saying, "I can think of few things that would hurt the interests of patients and the chiropractic profession as much as starting to warn patients of the risk of stroke."

By 1994, the message had changed. Chiropractors were told "there is a growing legal duty to disclose any known risk of serious harm, such as stroke or death, no matter how remote."

But four years later in 1998, after a 20-year old Saskatchewan woman, Laurie Mathiason, died from a stroke following a neck manipulation, a CTV News hidden camera investigation found many chiropractors were still not warning patients. One said there was no risk at all.

W-FIVE decided to see what patients are being told now given the public fight with neurologists. Chiropractors were picked randomly out of the Toronto phone book.

This time, our associate producer was asked to sign a consent form and was told about the risk, as the chiropractors see it.

"It's the same as getting hit by lightning or winning the lottery but it can happen," says the chiropractor.

W-FIVE's researcher did not get a neck adjustment but after an initial examination was told she didn't appear to be someone who should worry about stroke. The Canadian Chiropractic Association believes it is possible to screen patients.

"Now to be sure that you're not one of the patients at risk, I'm going to do a very thorough health history. I'm going to do a very thorough examination. I may even do X-rays," says Gorchynski, "They must do it the education process that graduates chiropractors gives all of them that skill and that depth of knowledge."

At the Chiropractic College, Kopansky-Giles demonstrates one technique she says is standard procedure for her and is taught to students. After safely extending the neck, she checks to see if the patient feels dizzy or light headed.

"I'm looking for vibrating back and forth in the irises question."

Some medical doctors say checking irises to determine if an artery could tear is simply ridiculous. And according to the chiropractors own research, patients who might be at risk are generally young and healthy and "cannot be identified by clinical or radiological examination."

No one can accurately predict if or when an artery will tear and that's why the neurologists are speaking out against neck manipulation and took an unprecedented step.

Sixty-three specialists from across the country signed their names to a public letter warning Canadians about the danger of neck manipulation.

"This is not a personal attack on chiropractors. This is not an emotional attack on the chiropractic profession. This is looking at the scientific evidence as it is accumulating in the 21st century," says Dr. Brad Stewart.

But the chiropractors do take it personally. The Canadian Chiropractic Association fired off a threatening letter warning the neurologists to back off, calling their concerns "seriously misleading and defamatory".

A group of doctors are now on the lookout for cases they might have missed, cases like Beryl Cronin.

Cronin went to chiropractors for 30 years because of knee and hip problems. The treatments did help. She had many neck manipulations without incident until last year when she had a minor stroke after her last adjustment, leaving her with balance and speech damage.

"I'd read the waiver but you never really think it's going to happen to you," says Cronin.

Dr. Stewart discovered a torn artery in her neck he believes was caused by her chiropractic treatment. He's calling on his colleagues to document all suspected cases.

But Dr. Stewart is not telling patients to stay away from chiropractors. He's telling chiropractors to stay away from necks.

"I say from [the shoulders] down is just fine but rapid, high velocity manipulation of the neck, which is the one most consistent with stroke, should not be done."

It's not just neurologists who are worried. There are chiropractors that have stopped performing neck adjustments because of the risk. But they're afraid to speak publicly about their change of practice and afraid of repercussions from their profession.

Not one of those chiropractors would agree to appear on W-FIVE.

Florence Limage wants people to think twice. Her husband went to a chiropractor for a routine treatment and ended up permanently disabled.

"Les was so full of life, enjoying his grandchildren... Our lives have been destroyed and the future for Les is not good."

Most chiropractors say they will continue to do neck manipulations because they're safe.

"People want us to continue to do what we do for them because they experience the benefit," says Gorchynski.

Diane Rodrigue agrees that patients might experience benefits. But she wants to remind them that it could also go the other way. They could end up like her.