As part of a multi-year evaluation of the Healthy Kids program in Los Angeles, we analyzed service utilization of Healthy Kids enrollees ages 0 to 18 using health plan encounter and claims data and assessed these data for completeness. Results suggest that actual service rates are higher than administrative data indicate. Other evidence from the evaluation suggests that some services are likely reimbursed by Restricted/Emergency Medi-Cal, and other services are provided just prior to enrolling in Healthy Kids. As a result, some encounters are not captured in health plan data for Healthy Kids, and will present challenges for ongoing program monitoring.