This study is a multi-center, single-blinded RCT. Adolescents (12-18 years old) with (s)PTSD will be randomly allocated by an independent researcher to the BITT (n=50) versus a waitlist control group (WLCG; n=50), stratified by center. Measurements are done at comparable time intervals for both groups: at pre-treatment (T0), directly after BITT or WLCG (T1) and at 3 (T2), 6 (T3) and 9 (T4) months follow-up. The WLCG receives BITT after the 3 months follow-up.