Americans, insured and not, make ample use of hospital emergency rooms: One out of every five visited an E.R. at least once in 2007, the latest year for which the National Center for Health Statistics has data.

Among the uninsured, 7.4 percent made two or more visits to an E.R., but so did 5.1 percent of people with private insurance. Medicaid recipients were the heaviest users of E.R.’s, with 15.3 percent of them making two or more visits during the year.

Adults in fair or poor health were most likely to go to an E.R. More than a third of them visited an emergency room at least once during the year.

People younger than 65 who said the E.R. was their only health care facility were no more likely to have gone to an emergency room than others, and for those older than 65, there were more E.R. visits by people with a usual source of care than by those without one.