(Get the facts and the verdict after the jump)
The Facts: The figure has been disseminated by the Pacific Research Institute, a conservative think tank that opposes the Obama administration's push for health-care reform. But Rowena Itchon, a spokeswoman for the institute, said the number was drawn from a 2003 study by the insurance company Blue Cross-Blue Shield.
That study concluded that a third of the uninsured - more than 14 million people - qualified for existing government programs such as Medicare and Medicaid, but were not enrolled in them. About another 13 million had incomes of $50,000 or more, suggesting they could obtain insurance on their own.
Nearly 6 million were what Blue Cross called "short-term uninsured," meaning people who are either between jobs or are just entering the work force. Many of the remainder were low-wage workers in firms with fewer than 10 workers, who could obtain coverage if the government offered tax credits for small businesses or grants to states, while others are illegal immigrants, it said.
Citing that research and other census data, PRI President Sally Pipes argued in a widely circulated 2008 opinion piece that only 8 million people - just under 3 percent of the U.S. population - are "chronically uninsured."
But the Census Bureau's survey - which found about 15 percent of the U.S. population uninsured - is the largest and most regular survey, said Karyn Schwartz, a senior policy analyst at the nonprofit and nonpartisan Kaiser Family Foundation. And according to its findings, "The bulk of the uninsured are U.S. citizens, they're from working families, but they have low incomes and would likely have trouble affording private coverage," she said.
The latest Census Bureau survey was published in 2008, based on data gathered in 2007. That survey does not take into account effects of the current recession, which officially began in December 2007.
The Verdict: In dispute - but most researchers who study health care issues rely on the Census Bureau's figures.