New analysis of the 2003 Commonwealth Fund Biennial Health Insurance Survey reveals that an estimated 77 million Americans age 19 and older--nearly two of five (37%) adults--have difficulty paying medical bills, have accrued medical debt, or both. Working-age adults incur significantly higher rates of medical bill and debt problems than adults 65 and older, with rates highest among the uninsured. Even working-age adults who are continually insured have problems paying their medical bills and have medical debt. Unpaid medical bills and medical debt can limit access to health care: two-thirds of people with a medical bill or debt problem went without needed care because of cost--nearly three times the rate of those without these financial problems.