CBT for PTSD (plus addiction treatment-as-usual) vs. IAC (plus addiction treatment-as-usual): 1) Reduces PTSD symptoms; 2) Improves addiction treatment retention; and, 3) Reduces substance use and severity. A hierarchy of effects is hypothesized. The target of the CBT is PTSD symptoms, which if reduced, will favorably leverage both treatment retention and substance use, above and beyond the equivalence in type and amount of treatment in both conditions.