In early 2003 San Mateo County, California launched the Children's Health Initiative (CHI), a program to ensure that 100 percent of children have access to comprehensive health insurance coverage. This first annual CHI evaluation report shows that, in its early months, the CHI achieved rapid enrollment growth in its new insurance product, "Healthy Kids." Utilization of services was low in the initial months. This successful outreach and enrollment is a product of intensive and sustained collaboration among the CHI partners. Future evaluation reports will document the impact of the program on access to care and cost.