OBJECTIVE: The purpose of this work was to identify the proportions of publicly (Medicaid and State Child Health Insurance Program) insured and uninsured children who did not identify a usual source of care from 1998 to 2006, spanning the State Children's Health Insurance Program (1997 to present) and the President's Health Center Initiative (2002 to present), and to characterize unmet medical need as it relates to insurance and a usual source of care for publicly insured and uninsured children. METHODS: We conducted a secondary data analysis of multiple years of the National Health Interview Survey. We identified the proportion of publicly insured and uninsured children aged 0 to 17 years who did not identify a usual source of care and stratified according to the site of care. We described the odds of reporting an unmet medical need according to insurance status and usual source of care, compared with privately insured children with a usual source of care. Sample weights were used to derive national estimates. RESULTS: From 1998 through 2006, there were significant increases in the proportions of children enrolled in Medicaid (16.7%-24.5%) and the State Child Health Insurance Program (2.0%-5.3%). The proportion of uninsured children has remained stable from 2002 to 2006 at approximately 10%. However, the proportion of uninsured reporting no usual source of care increased from 17.8% to 23.3%. Hispanic children had significant increases in the proportions of the uninsured and reporting no usual source of care by 2006. Hispanics constituted the largest proportion in both groups. Uninsured children and children without a usual source of care reported the highest odds of unmet need. Among the insured, publicly insured children had twice the odds of reporting an unmet need compared with privately insured children. CONCLUSIONS: During the State Child Health Insurance Program and the President's Health Center Initiative, growing proportions of uninsured children reported no usual source of care. Unmet medical need was the highest for the uninsured and those without a usual source of care. These findings suggest that initiatives designed to improve access to care must combine broadened insurance coverage with enhanced access to usual sources of care.