Introduction: Although evidence-based treatments for posttraumatic stress disorder (PTSD) in adolescents and young adults exist, affected youth do not have sufficient access to these treatments due to structural and attitudinal barriers. Internet- and mobile-based interventions (IMIs) can help fill this healthcare gap, but such programmes have not yet been sufficiently evaluated in youth with PTSD. Aim: This study aims to investigate the feasibility of an IMI for youth with PTSD in a one-arm, non-randomised, prospective...