--- - |2+ Abstract Objective The aim was to investigate whether clinical experience, formal cognitive behavioural therapy (CBT) training, adherence, and competence predict outcome in CBT for anxiety disorders in youth. Method Videotapes (N = 181) from the sessions in a randomized controlled effectiveness trial (Wergeland et al., 2014, Behaviour Research and Therapy, 57, 1–12) comprising youth (N = 182, M age = 11.5 years) with mixed anxiety disorders were assessed for treatment adherence and competence using the Competence and Adherence Scale for CBT for anxiety disorders in youth (Bjaastad et al., 2016, Psychological Assessment, 28, 908–916). Therapists' (N = 17) clinical experience and educational background were assessed. Participants completed a diagnostic interview (Anxiety Disorders Interview Schedule, child and parent versions) and an anxiety symptom measure (Spence Children's Anxiety Scale, child and parent versions) at pretreatment, posttreatment, and 1‐year follow‐up. Results Higher therapist adherence was related to better treatment outcomes, whereas number of years of clinical experience and competence was related to worse outcomes. However, these findings were not consistent across informants and the time points for the assessments. Interaction effects suggested that competence among therapists with formal CBT training was related to better patient outcomes. Conclusions Therapist adherence, competence, and clinical experience are associated with outcomes of manualized CBT for youth anxiety disorders, but mixed findings indicate the need for more research in this area. - Clinical Psychology & Psychotherapy, EarlyView.