The US Supreme Court has upheld the heart of President Barack Obama's health care overhaul, handing him a huge election-year political victory and keeping in force the legislative centrepiece of his term, a law aimed at covering more than 30 million uninsured Americans.
The decision means the historic overhaul, opposed by virtually all Republicans including Mitt Romney, Mr Obama's challenger, will continue to go into effect over the next several years, affecting the way that countless Americans receive and pay for their medical care.
The decision, written by conservative Chief Justice John Roberts, sided with Mr Obama on the centrepiece of the law, which requires all Americans to have health insurance or face a federal fine.
"Whatever the politics, today's decision was a victory for people all over this country," Mr Obama said.
"It should be pretty clear by now that I didn't do this because it was good politics," he said. "I did it because it was good for the country."
By letting the law stand, the decision keeps the United States on a course toward joining all other major developed countries in guaranteeing health care for all its citizens.
Republicans, with an eye on the upcoming presidential election, were quick to respond. Mr Romney said his mission now was to see the overhaul repealed, calling the changes in the system "bad law".
Republican Party chairman Reince Priebus said: "Today's Supreme Court decision sets the stakes for the November election. Now, the only way to save the country from ObamaCare's budget-busting government takeover of health care is to elect a new president."
Republican House Speaker John Boehner said the health care law makes it harder for small businesses to hire workers. "Today's ruling underscores the urgency of repealing this harmful law in its entirety," he said.
Stocks of hospital companies rose after the decision was announced, while shares of insurers fell sharply. Shares of drugmakers and device makers fell slightly.