Basically. the justices said that the individual mandate -- the requirement that most Americans buy health insurance or pay a fine -- is constitutional as a tax.
Chief Justice John Roberts -- a conservative appointed by President George W. Bush -- provided the key vote to preserve the landmark health care law, which figures to be a major issue in Obama's re-election bid against Republican opponent Mitt Romney.
Obama is expected to comment on the decision within the next two hours.
The government had argued that Congress had the authority to pass the individual mandate as part of its power to regulate interstate commerce; the court disagreed with that analysis, but preserved the mandate because the fine amounts to a tax that is within Congress' constitutional taxing powers.