The goal of this observational study is to learn about the level of change in post-traumatic stress symptoms in adolescents with traumatic experiences over the course of trauma-focused cognitive behavioral therapy for children and adolescents according to Cohen, Manarinno, & Deblinger (2017).

Participants will be included if:

1. they are between 12 and 18 years of age;
2. they have been exposed to at least one or more traumatic event(s) according to the DSM-5 A criteria after the age of 3 years and dating back at least 1 months (with regard to the ability of patients to remember the event(s) and to the high spontaneous remissions of PTSS in the first month after a traumatic event);
3. they exhibit high severity of DSM-5 PTSS as indicated by a total symptom score of ≥25 assessed with the Child and Adolescent Trauma Screen 2 (CATS-2);
4. a nonoffending adult caregiver is available for the treatment and willing to participate in weekly treatment sessions (the inclusion of a caregiver is integral to the TF-CBT treatment model);
5. they are willing and able to attend weekly treatment sessions;
6. if their living circumstances are safe and stable to minimize the risk of re-traumatization during the project;
7. they and their caregiver have sufficient command of the German language (i.e., to participate in assessment [read] and treatment[converse]);
8. they and their caregivers possess a smartphone.
9. they and their caregiver provided written informed consent.

Participants will not be included if:

1. they exhibit acute suicidal behavior or have suicidal ideations requiring immediate hospitalization;
2. they have a documented developmental disorder (i.e., autism spectrum disorder) or current psychosis based on adolescent- and caregiver-report and clinical assessment;
3. they exhibit severe substance misuse based on clinical assessment;
4. take part in concurrent psychotherapy during TF-CBT;
5. exhibit severe intellectual disability based on clinical assessment.

Adolescents between 12 and 18 years for whom trauma-focused treatment is indicated due to a PTE/ PTEs they have experienced as well as a significant level of PTSS.