For the study, Cathy Schoen, president for research and evaluation at the Commonwealth Fund, and colleagues surveyed about 3,500 adults between June 2007 and October 2007. About three-fourths of the adults were between ages 19 and 64. The study defined as underinsured adults who had health insurance all year but had out-of-pocket medical costs equal to at least 10% of their annual incomes or greater than 5% for those with low incomes, as well as those who faced deductibles greater than 5% of income.

The study found that 25 million U.S. adults -- about one in every five younger than age 65 -- were underinsured in 2007, compared with 16 million in 2003. According to the Times, people generally receive generous health insurance through large companies had adequate coverage, but coverage through small companies or the non-group market is increasingly characterized by high deductibles or limited benefits.

Forty-five percent of the underinsured adults reported that they had problems with payment of their medical bills, were contacted by collection agencies about bills or changed their lifestyles to pay medical costs, compared with 51% of uninsured adults and 21% of those with adequate health insurance, the study found. About 53% of underinsured adults said that they went without necessary medical care because of cost issues, compared with 68% of uninsured adults and 31% of those with adequate health insurance, according to the study.