A growing body of research demonstrates the many benefits of expanded public coverage for children. Expansions in Medicaid and the State Children's Health Insurance Program (SCHIP) have helped to increase insurance coverage, increase access to care, and reduce the financial burdens facing low-income families. Less attention has been focused on the cost of expanding public coverage. We argue that budgetary data may exaggerate the net costs of these expansions because many of the highest-cost children would have received publicly funded care even if the expansions had not taken place. Using data from the 2000 Medical Expenditure Panel Survey, we simulate the net cost of SCHIP, finding that the true cost of this program-both to states and to the federal government-is substantially less than average spending per enrollee would suggest. Our results strengthen the benefit-cost argument against implementing rollbacks in SCHIP.