Uninsurance among State Children's Health Insurance Program (SCHIP)--eligible children was examined using the 2001 National Survey of Children with Special Health Care Needs. Nationally, 6.1% of children (4.3 million) were eligible for SCHIP in 2000, and 35.6% (1.5 million) eligible children were uninsured. In addition to the variation across states in SCHIP eligibility and uninsurance, the study revealed a lower uninsurance rate in the 17 states that expanded Medicaid eligibility, compared with the 34 states with separate SCHIP programs that were implemented alone or in combination with Medicaid expansion. It was also revealed that the parents of SCHIP-eligible but uninsured children had limited knowledge of and experience with SCHIP.