TORONTO – Canada’s Supreme Court yesterday struck down a Quebec law that banned private insurance for services covered under Medicare, a landmark decision that could affect the country’s universal health-care system.

The justices took a year to rule on a case that began in 1997, when an elderly Montreal man, George Zeliotis, tried to pay for hip replacement surgery rather than wait nearly a year for treatment at a public hospital.

Mr. Zeliotis told the high court that he suffered pain and became addicted to painkillers during the year-long wait for surgery, and he should have been allowed to pay for faster service with private insurance.

“It is indeed a historical ruling that could substantially change the very foundations of Medicare as we know it,” the president of the Canadian Medical Association, Dr. Albert J. Schumacher, said.

Although the ruling was made on the Quebec law, it likely will affect other Canadian provinces that forbid residents from buying private health-care insurance for treatment under the country’s Medicare system.

Opponents of changes to Medicare claimed it could force Canada into a two tiered health-care system in which those who have deeper pockets get faster, better service from doctors who opt out of the public health-care program.

Mr. Zeliotis’s doctor, Jacques Chaoulli, argued that his patient’s constitutional rights were violated because Quebec could not provide the care he needed and did not offer him the option of getting it privately.

Dr. Chaoulli also argued that doctors should be allowed to open private hospitals if patients are willing to pay.

The 1984 Canada Health Act affirmed the federal government’s commitment to provide mostly free health care to all, including the more than 200,000 immigrants arriving each year, under a system called Medicare.

But the universal health-care system – while considered one of the fairest in the world – has been plagued by long waiting lists and a lack of doctors, nurses, and new equipment. Some patients wait years for surgery, MRI machines are scarce, and many Canadians travel to America for medical treatment.

In most Canadian provinces, it is illegal to seek faster treatment and jump to the head of the line by paying out of pocket for public care. Private health clinics have sprouted up even though they are technically illegal, though the provincial governments tend to look the other way.

If Mr. Zeliotis had been from outside Canada, he could have bought treatment in a private Quebec clinic. That is one way the system discourages the spread of private medicine – by limiting it to nonresidents.

Most polls indicate Canadians support Medicare, despite the high taxes needed to fund the service, seeing it as a marker of egalitarianism and independent identity that sets their country apart from America, where about 45 million Americans lack health insurance.