Despite the fact that youth involved in the child welfare (CW) and runaway and homeless youth (RHY) systems are particularly vulnerable to being trafficked, there is no consensus screening tool to identify trafficking experiences among such youth. In order to better serve youth trafficking victims, this study developed a Human Trafficking Screening Tool (HTST) and pretested it with 617 RHY- and CW-involved youth. This research established that the screening tool is accessible to youth and easy to administer, and that both the full-length tool and a shorter version were effective in identifying youth who are trafficking victims in RHY and CW systems, though additional research with more youth is needed.