The number of illegal immigrants in the United States who lack health insurance is a source of controversy in the debate over President Barack Obama's plan to overhaul the $2.5 trillion healthcare sector.
Critics of Obama's effort accuse the government and media of undercounting illegal immigrants to inflate the percentage of uninsured Americans within those who report being uninsured -- and make the need for reform more urgent.
U.S. healthcare costs are higher because illegal immigrants who lack insurance and don't pay taxes drain resources through trips to emergency rooms and clinics, they say.
Supporters of the Obama plan play down the overall impact that illegal immigrants have on the healthcare sector.
Here are some facts about illegal immigrants and healthcare in the United States:
* There were 46.3 million people without health insurance in the United States in 2008 from 45.7 million a year earlier, according to the Census Bureau's Current Population Survey released on Thursday.
* A total of 9.5 million among the uninsured said they were "not a citizen" in 2008, down from 9.7 million one year earlier. Foreign students and legal immigrant workers as well as illegal immigrants are included in this group.
* Some 44.7 percent of non-citizen immigrants were uninsured in 2008. Among native-born citizens, the figure stood at 12.9 percent in 2008.
* Non-citizen immigrants are around three times as likely to be uninsured as native born citizens.
* Some 21.3 million people said they were not citizens in 2008 census data, down from 22.2 million in 2007 data.
The decline could be caused by accelerated naturalization, a drop in the number of immigrants because of the economic climate or fewer people answering truthfully, said Leighton Ku, professor of public policy at George Washington University.
* There are 6.1 million uninsured adults who are illegal immigrants and 700,000 uninsured illegal immigrant children, according to an estimate by the non-partisan Pew Hispanic Center, which was based on 2007 Census data.
* U.S. citizens accounted for the bulk of the 8.6 million additional people who became uninsured between 2000 and 2006, according to survey data. Two million of these were non-citizens, while half a million were naturalized citizens.
* Some 20 percent of adult citizens went to an emergency room in the last year, compared to 13 percent of non-citizen adults.
* Illegal immigrants work disproportionately in jobs that do not provide health insurance.
* There is no widely accepted national estimate of the annual cost of healthcare for illegal immigrants, partly because hospitals do not collect immigration figures.
The Federation for American Immigration Reform, which advocates a temporary moratorium on most immigration, puts the cost at $10.7 billion and calls the estimate conservative.
Sources: U.S. Census Bureau; Pew Hispanic Center; Kaiser Commission on Medicaid and the Uninsured; Center for Immigration Studies; Leighton Ku, professor of public health policy, George Washington University; Federation for American Immigration Reform; Migration Policy Institute.
(Writing by Matthew Bigg, editing by Todd Eastham)