Objective: Posttraumatic stress disorder (PTSD) following interpersonal trauma in transitional-aged youth (TAY), aged 15 to 25, is highly prevalent; however, evidence-based interventions have rarely been studied. Method: A single-group pre-/posttest study was conducted at headspace Sunshine, Melbourne, Australia, evaluating the feasibility, acceptability, safety, tolerability, and potential clinical effectiveness of trauma-focused cognitive–behavioral therapy (TF-CBT). Results: An intent-to-treat analysis was conducted for N = 20 participants (65% female, n = 13) who attended a mean of 15 TF-CBT sessions over 25 weeks. At the end of treatment, only 1 of the 16 participants with a baseline PTSD diagnosis still met diagnostic criteria. Significant improvements were also noted for self-report measures of PTSD (d = –.83), anxiety (d = –.74), and depression (d = –.76). A minority of participants reported a brief exacerbation in symptoms of PTSD (n = 8) and anxiety and depression (n = 5) during stabilization and directly before and/or after the trauma-narration phase. However, all symptoms resolved at the end of treatment. The majority of participants (85%, n = 17) rated the intervention as helpful. Conclusion: Regardless of the expected temporary symptom exacerbation, the results indicated that TF-CBT was safe, tolerable, and acceptable. Transitional-aged youth is an emerging area of research. With limited research available on this age group to inform evidence-based practice, it is recommended that a randomized controlled trial is conducted to determine if TF-CBT (Cohen et al., 2017) can be effectively translated to this underresearched age group.