This study examined the relationship between placement change and outpatient mental health service use. It is based on (1) conceptual propositions about the impact of the foster care living context on mental health service use, and (2) empirical knowledge about the adverse consequences of placement change. Results of the study, which were based on a cohort of 570 children in foster care in San Diego County, suggest an association between placement changes in child welfare and use of outpatient mental health services. Specifically, an increase in the number of placement changes predicted a greater rate of outpatient mental health visits. The study further found that children who experienced behavior-related placement changes received more outpatient mental health visits than children who experienced placement changes for other reasons. Follow-up analyses of the 144 children who experienced any behavior-related placement changes further indicated that the rate of outpatient mental health service use almost doubled in the 90 days following the first behavior-related placement change. Findings from this study have implications for the practice, policy and research fields in child welfare as well as mental health.