This systematic review aimed to (1) identify and summarize empirical studies on youth with behavioral health disorders aging out of foster care and (2) address implications for behavioral health policy, research, and practice. We identified previous studies by searching PubMed, PsycINFO, EBSCO, and ISI Citation Indexes and obtaining references from key experts in the child welfare field. A total of 28 full articles published between 1991 and 2014 were reviewed and summarized into the key areas including systems of care, disability type, transition practice area, study methods, study sample, transition outcome measures, study analysis, and study findings. Considering how fast youth who have behavioral health disorders fall through the crack as they exit foster care, one cannot understate the importance of incorporating timely and appropriate transition planning and care coordination for youth who have behavioral health disorders aging out of foster care into the usual case management performed by behavioral health systems and service providers.