Multiple agencies at the federal and state level provide for children with special health care needs (CSHCN), with variation in eligibility criteria. Epidemiological studies show that 3.8%-32% of children could be classified as children with special health care needs, depending on the definition and method of determination used. OBJECTIVES: To determine the extent of variation between definitions used and funding by Supplemental Security Income (SSI), Title V, and Medicaid for CSHCN. METHODS: Statistics on children receiving SSI and the amount of funding were obtained from the SSI website. This was compared to information on Title V children from the Maternal and Child Health Bureau (MCHB) website and eligibility definitions published by the Institute of Child Health Policy in Gainesville, Florida. Medicaid definitions were obtained through interviews with state Medicaid agencies and confirmed with state regulations. RESULTS: The population enrolled in SSI has varied with alterations in eligibility criteria. The number of children enrolled in SSI and the amount of funding per child in each state correlate with the state poverty rate (r=0.56, p<0.0001; r=0.44, p<0.001). Enrollment in Title V does not correlate with state poverty rates (r=0.16, p=0.25). Title V definitions vary widely among states, but there was no correlation between the number of children served or amount of funding per child and the type of definition used (Z=-0.12, p=0.91; Z=-0.59, p=0.55). State Medicaid agencies rarely define CSHCN. CONCLUSIONS: There is significant variation in definitions used by agencies serving CSHCN. Agencies need to be more explicit with eligibility criteria so the definitions are logical to those making referrals for services.