Young people in care (i.e., in the child welfare system) are a group who have often experienced very high rates of potentially traumatic events, including maltreatment. It is well-documented that they have high rates of trauma-related mental health difficulties, such as posttraumatic stress. To address the needs of the large number of young people who may benefit from support, scalable interventions are crucial. But also important is that they are effective and deliverable - particularly given the complexity of this group and services. We assessed a five-session group CBT-based intervention for PTSD. The primary goal was to understand core procedural and protocol uncertainties to address prior to a definitive trial. Participants were 34 10-17 year olds in care, with moderate to severe posttraumatic stress symptoms, and their caregiver. We ran seven groups (four online), delivered in social care and NHS-based mental health teams. Data were collected via pre-, post-, 3-month follow-up questionnaires and qualitative interviews. Of the 34 participants allocated to the intervention, 27 (80%) attended at least three of the five sessions (most attended all). Caregiver attendance was lower (50%). There was generally good completion of assessment measures. Qualitatively, most participants were positive about the intervention, and many reported improvements in areas such as coping, sleep, and willingness to talk about experiences. However, there were important concerns about the lack of ongoing support, given this was a low-intensity intervention for a group who often had complex needs. The intervention and research protocols were acceptable to most young people and carers. With modifications, a future definitive trial would likely be possible. However, key considerations include: how (and whether) to screen for PTSD; the trial design; and the option to embed high-intensity support (e.g., via assessing a stepped-care model).