Abstract:Objective: Residual symptoms are common following posttraumatic stress disorder (PTSD) treatment. Despite the high prevalence of and poor outcomes associated with co-occurring PTSD and alcohol use disorder (AUD), only one study has examined residual symptoms following psychotherapy in a comorbid sample. Method: Veterans (N = 71) with PTSD and AUD were randomized to receive prolonged exposure therapy (PE) with placebo (PE + PLA) or topiramate (PE + TOP). PTSD and depressive symptoms were assessed at pre- and posttreatment. Frequency counts were calculated for each residual symptom. Fisher’s exact tests examined whether the percentages of participants endorsing residual symptoms differed by treatment condition, loss of PTSD diagnosis, and improvement in heavy drinking. Results: Residual symptoms were commonly endorsed across PTSD symptom clusters. Participants who received PE + TOP endorsed fewer residual depression (ORs = 0.27–0.30) and PTSD symptoms in the alterations in mood/cognition cluster (ORs = 0.26–0.35) than those who received PE + PLA. Relative to those who retained their PTSD diagnosis, those who lost the diagnosis were less likely to endorse most residual PTSD and depression symptoms. No differences in residual symptoms were observed between those who did and did not improve in their heavy drinking. Conclusions: The residual symptoms most likely to persist may depend on the treatment being evaluated; topiramate may have unique effects on depressionogenic symptoms while patients are taking the medication. Residual symptoms may signal a need for additional treatment if they are distressing/functionally impairing. More work is needed to understand whether symptoms are maintained or continue to improve longitudinally.