Exposure to traumatic events, such as automobile accidents and assault, can cause individuals to develop persistent psychological difficulties such as post-traumatic stress disorder (PTSD). PTSD is an anxiety disorder characterized by avoidance, hyperarousal symptoms, and mental re-experiencing of the traumatic event. PTSD is a serious condition that may cause social and psychological impairment; therefore, safe and effective treatments are needed. Both CBT and antidepressant therapy have been shown to effectively treat PTSD symptoms; however, comparisons of the treatments are limited. This study will compare the short- and long-term effectiveness of CBT and the antidepressant sertraline.