The aim of this study was to index the long-term benefits of early provision of cognitive behavior therapy to trauma survivors with acute stress disorder. Civilian trauma survivors (n = 80) with acute stress disorder were randomly allocated to either cognitive behavior therapy (CBT) or supportive counseling (SC) - 69 completed treatment, and 41 were assessed four years post-treatment for post-traumatic stress disorder (PTSD) with the Clinician Administered PTSD Scale. Two CBT patients (8%) and four SC patients (25%) met PTSD criteria at four-year follow-up. Patients who received CBT reported less intense PTSD symptoms, and particularly less frequent and less avoidance symptoms, than patients who received SC. These findings suggest that early provision of CBT in the initial month after trauma has long-term benefits for people who are at risk of developing PTSD.