Therapist behaviour influences group cohesion and the outcome of group psychotherapy. The group members make first hand observations of the therapists in action, and experience the benefit or adversity from it. This study explores patients’ experiences of therapist behaviour and how it is helpful and hindering for progress in cognitive behavioural therapy groups for anxiety and depression. We interviewed 23 patients from 17 different CBT groups. The fully transcribed texts were analyzed using Braun & Clarke’s thematic analysis with blinded double coding of 26% of the material. The resulting themes were (1) the co-therapists, (2) the way to communicate, (3) the session structure, and (4) the therapists as group facilitators. Helpful and hindering aspects were highlighted in each theme. A novel finding of the study was the importance of the interaction between the two co-therapists, which was underscored by the patients’ investment in attempts to make meaning of their interplay when it was not harmonic. As previously described, helpful aspects of therapist behaviour included: concise communication delivered in an empathic way, ability to structure sessions flexibly and the facilitation of group cohesion. The results add to our understanding of the therapists’ complex role in CBT groups and they should inform future group therapist training.