He called the decision incorrect and said Thursday that it is "bad law." He says it raises taxes and cuts Medicare.
Romney says that, if elected in November, he will work to repeal and replace the law. But he hasn't said precisely how.
As Massachusetts governor, Romney signed into law a measure that required all state residents to have health coverage. That notion was the cornerstone of the law enacted by President Barack Obama and congressional Democrats. The high court decided it was constitutional.