This study investigated the temporal course of improvement in PTSD and alcohol dependence symptoms among individuals participating in a 12-week outpatient treatment study. Participants were 94 individuals with comorbid PTSD and alcohol dependence enrolled in a double-blind, placebo-controlled medication trial. Outcome measures included PTSD symptoms (as measured by the Clinician Administered PTSD Scale, Impact of Events Scale, and Civilian Mississippi Scale for PTSD) and alcohol use severity (as measured by the Time Line Follow Back). Study completion rates were significantly higher for individuals who demonstrated improvement in both disorders. Improvements in PTSD had a greater impact on improvement in alcohol dependence symptoms than the reciprocal relationship. Improvement in hyperarousal PTSD symptoms, in particular, was related to substantially improved alcohol use. Examination of the temporal course of symptom improvement revealed that alcohol symptoms tended to start improving either before or in conjunction with PTSD symptoms. Although preliminary in nature, these findings suggest that co-occurring PTSD symptoms may have a strong impact on alcohol dependence treatment outcome, and that PTSD treatment may be important to optimizing outcomes for patients with comorbid PTSD and alcohol dependence.