Adult research has demonstrated the efficacy of selective serotonin reuptake inhibitors (SSRIs) in decreasing Posttraumatic Stress Disorder (PTSD) symptoms; to date the SSRIs are the only medication class with demonstrated efficacy in treating all three PTSD symptom clusters (reexperiencing, avoidance, and hyperarousal). No studies have evaluated the impact of SSRIs on PTSD symptoms in children or adolescents. Trauma-focused CBT has been shown in several studies to be efficacious in decreasing PTSD symptoms in sexually abused children and adolescents. Many children and youth with PTSD are currently prescribed SSRIs and other medications. This study will evaluate whether adding the SSRI sertraline provides additional benefits over TF-CBT treatment for sexually abused children and adolescents with PTSD. If adequate numbers of children with comorbid PTSD and depressive and/or anxiety disorders are included, it may also be possible to evaluate whether any benefit of adding sertraline is restricted to those children with comorbid disorders.