Patients admitted to the participating addiction treatment programs are routinely screened for PTSD using a brief self-report survey, the PTSD Checklist (PCL). These forms are collected by clinical staff of the treatment program and scored for PTSD diagnostic criteria. Patients scoring 44 or greater on the PCL are approached by a clinic staff about potential interest in the study. If they wish to learn more about the study, the research coordinator (an on-site employee) is contacted, a suitable time arranged, and the patient engaged in the process of informed consent.