Objective: To evaluate the efficacy of individual trauma-focused cognitive-behavioral therapy (CBT) for treating posttraumatic stress disorder (PTSD) in children and young people. Method: Following a 4-week symptom-monitoring baseline period, 24 children and young people (8-18 years old) who met full "DSM-IV" PTSD diagnostic criteria after experiencing single-incident traumatic events (motor vehicle accidents, interpersonal violence, or witnessing violence) were randomly allocated to a 10-week course of individual CBT or to placement on a waitlist (WL) for 10 weeks. Results: Compared to the WL group, participants who received CBT showed significantly greater improvement in symptoms of PTSD, depression, and anxiety, with significantly better functioning. After CBT, 92% of participants no longer met criteria for PTSD; after WL, 42% of participants no longer met criteria. CBT gains were maintained at 6-month follow-up. Effects of CBT were partially mediated by changes in maladaptive cognitions, as predicted by cognitive models of PTSD. Conclusions: Individual trauma-focused CBT is an effective treatment for PTSD in children and young people. (Contains 2 tables and 2 figures.)