The five largest insular areas of the United States--American Samoa, the Commonwealth of the Northern Mariana Islands (CNMI), Guam, Puerto Rico, and the U.S. Virgin Islands--receive federal funding through Medicaid and the State Children's Health Insurance Program (CHIP), joint federal-state programs that finance health care for certain low-income individuals. These programs are administered and funded differently in the insular areas when compared to the states. The U.S. Senate Subcommittee on Health Care Committee on Finance asked the Government Accountability Office (GAO) to examine the Medicaid and CHIP programs in the insular areas and to provide information on the availability of program-related data for the areas. Specifically, the GAO examined (1) Medicaid and CHIP income eligibility criteria used by the insular areas, (2) Centers for Medicare & Medicaid Services' (CMS) approach to collecting Medicaid and CHIP enrollment and spending data from the insular areas and its assessment of the reported spending data, and (3) the extent to which Current Population Survey (CPS) or American Community Survey (ACS) data are available for the insular areas. The GAO found that insular areas' Medicaid and CHIP income eligibility criteria vary, and contribute to wide variation in the estimated percent of the population covered by Medicaid in each of the insular areas. For example, two of the areas base their income eligibility criteria on the FPL, while two other areas base their income eligibility criteria on locally established income limits. To improve the availability of the data that could be used in a CHIP allotment formula, the GAO recommends that the Secretary of Commerce direct Census to update, between decennial censuses, the demographic data for American Samoa, CNMI, Guam, and the U.S. Virgin Islands. In written comments on a draft of this report, DOC agreed with this recommendation. Enclosures include: (1) Insular Areas Federal Medicaid Funding Caps (Amount in dollars) 1998-2008; (2) Insular Areas CHIP Allotments (Amount in dollars) 1998-2008; (3) Comments from the Department of Commerce; and (4) Comments from the Centers for Medicare & Medicaid Services. (Contains 2 figures, 1 table, and 46 footnotes.)