To evaluate the efficacy of individual trauma-focused cognitive-behavioral therapy (CBT) for treating posttraumatic stress disorder (PTSD) in children and young people.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.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.Individual trauma-focused CBT is an effective treatment for PTSD in children and young people.