Objectives. Alcohol use disorder (AUD) and posttraumatic stress disorder (PTSD) frequently co-occur, and having one condition worsens the course of the other. Individuals with both disorders exhibit worse functioning across a number of domains than individuals with either disorder alone. Prolonged exposure therapy (PE) is among the most effective treatments for PTSD. PE has been rated as a frontline treatment by multiple guidelines and reviews including the VA/DoD Clinical Practice Guidelines for the treatment of PTSD. However, in studies of individuals with PTSD and AUD, changes in alcohol use are only slightly better than in control or standard care conditions, reductions in PTSD symptoms are sometimes modest relative to studies of PE in PTSD patients without AUD, and rates of drop out from treatment are high. Combining PE with medication to curb drinking shows promise to improve upon the effectiveness of PE for individuals with comorbid AUD and PTSD, although thus far few studies have examined combining psychotherapy and medication. Topiramate is the single medication that has shown effectiveness for both AUD and PTSD and shows promise for reducing drinking among individuals with AUD and PTSD. However, the effect of adding topiramate to PE to treat comorbid AUD/PTSD has yet to be examined. The critical next step is to test a best practice PTSD treatment, PE, together with a promising pharmacological agent, topiramate, which has been found to be effective for both AUD and PTSD. Innovation: This application seeks to shift current clinical practice paradigms. A refinement to existing interventions is proposed through integration of two evidence based treatments.