The Affordable Care Act, including its individual mandate that virtually all Americans must buy health insurance, is constitutional according to an opinion issued by the United States Supreme Court June 28, 2012.
The interesting twist is this. There WEREN'T the required five votes to uphold it on the ground that Congress could use its power to regulate commerce between the states to require everyone to buy health insurance. However, five Supreme Court Justices DID AGREE under the taxing power of 26 U.S.C. 5000A that the penalty that someone must pay if he or she refuses to buy insurance is a kind of tax that Congress can impose using its taxing power.
Because the mandate survives, the Court did not need to decide what other parts of the statute were constitutional, except for a provision that required states to comply with new eligibility requirements for Medicaid or risk losing their funding. On that question, the Court held that the provision is constitutional as long as states would only lose new funds if they didn’t comply with the new requirements, rather than all of their funding.