In 2004, 89.4 percent of uninsured children who qualified for Medicaid or the State Children's Health Insurance Program lived in families who filed federal income tax forms. This substantially exceeds the proportion of uninsured but eligible children who can be reached through many other outreach strategies. Federal lawmakers could cover uninsured children in these families by: (a) changing federal income tax forms so parents can identify their uninsured children and request coverage; (b) investing in information technology allowing data exchange between states and the Internal Revenue Service; and (c) letting states cover uninsured children if tax information shows they qualify.