The US Supreme Court has upheld the heart of President Barack Obama's health care reforms, handing him a huge election-year political victory.
The ruling keeps 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, 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 personal 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.
Republicans, with an eye on the November presidential election, were quick to respond. "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," party Chairman Reince Priebus said in a statement.
Polls show a majority of Americans do not support the health care overhaul, which, ironically, was based on a plan put in place in Massachusetts when Mr Romney was governor there. The Massachusetts law has been widely supported by residents since it took effect in 2006.
While Mr Romney defends the Massachusetts plan, he had said such changes should be left to the individual states and not be imposed by the federal government. He has promised to revoke the health care overhaul if he wins the White House in November.
The law's centrepiece takes effect in 2014, at the same time that the law would prohibit insurance companies from denying coverage to people with existing health problems. Most experts had said the coverage guarantee would balloon costs unless virtually all people joined the insurance pool.
Most Americans already are insured. The law provides subsidies to help uninsured middle-class households pay premiums and expands federal health care for poor people.
The court did find problems with the law's expansion of Medicaid - federal-state health coverage for the poor - but even there, it said the expansion could proceed as long as the federal government does not threaten to withhold states' entire Medicaid allotment if they do not take part in the law's extension.