This article evaluates the use of cognitive-behaviour therapy with an 11-year-old boy who developed post-traumatic stress disorder (PTSD) after witnessing a violent incident which culminated in the death of a relative. Treatment involved a combination of imaginal exposure to scenes from the traumatic incident and in vivo exposure to associated feared situations. The intervention resulted in considerable improvement in the three key features of PTSD: re-experiencing the event (intrusive thoughts, nightmares and flashbacks); avoidance of associated stimuli; and levels of arousal.