This RCT investigated the long-term benefits of cognitive behaviour therapy (CBT) for trauma survivors with acute stress disorder by assessing patients 3 years after treatment. Civilian trauma survivors (n = 87) were randomly allocated to six sessions of CBT, CBT combined with hypnosis or supportive counselling (SC); 69 completed treatment and 53 were assessed 2 years post treatment for post-traumatic stress disorder (PTSD) with the Clinician-Administered PTSD Scale. In terms of treatment completers, two CBT patients (10%), four CBT/hypnosis patients (22%) and 10 SC patients (63%) met PTSD criteria at 2-year follow-up. ITT analyses indicated that 12 CBT patients (36%), 14 CBT/hypnosis patients (46%) and 16 SC patients (67%) met PTSD criteria at 2-year follow-up. Patients who received CBT and CBT/hypnosis reported less re-experiencing and fewer avoidance symptoms than patients who received SC. These findings point to the long-term benefits of early provision of CBT in the initial month after trauma.