In the United States, cost of health-care services is a barrier to accessibility of health care, and persons often do not seek medical care because of concerns about cost, regardless of whether they have health insurance. In addition, three fourths of persons in the United States who have difficulties paying their medical bills have some type of health insurance. Although the affordability of health care among persons without health insurance has been described, characterization of affordability among persons who are underinsured is limited. To determine state-specific estimates of the prevalence of persons aged 18-64 years who are either uninsured or underinsured using an experiential definition of underinsurance, CDC analyzed data from the Behavioral Risk Factor Surveillance System (BRFSS). This report summarizes the results of that analysis, which document variations in state-specific rates for adequate insurance coverage.