This study analyzed annual service use and payment data for children in racial/ ethnic subgroups in Medicaid Programs of four States, and compared service use of youth treated with mental health or substance abuse (MH/SA) conditions to youth without such conditions. In addition to geographic variation in rates (6.2 to 10.7 percent used MH/SA related care), results showed children who used MH/SA services to be disproportionately older, male, and white when compared with all Medicaid children. Examination of costs per claimant found costs for the MH/SA population of children to be three to six times greater than a comparison sample.