Children in foster care have lower health status than do their peers and limited access to health care. The Illinois Department of Children and Family Services developed HealthWorks, a separate primary care preferred provider system for children in foster care. This study compared claims data for children in HealthWorks with children not enrolled in HealthWorks and with children in Aid to Families with Dependent Children (AFDC) who had never entered foster care. Children enrolled in HealthWorks were more likely than were other children to receive all of the services except general inpatient hospitalizations. They had greater odds of receiving general exams and physicians' services and were more likely to visit the emergency room than children who were not enrolled. They were more likely to receive all of the measured services when compared with children receiving Medicaid through AFDC.