It is still an open question whether psychotherapists adhere to their therapeutic conceptions in routine practice (clinician's treatment adherence) and thus to what extent the two most common approaches, cognitive-behavioural (CBT) and psychodynamic therapy (PDT), differ from each other as theoretically expected (treatment differentiation). This holds true especially in case of group therapy.The study compares essential process components of CBT and PDT group treatments under clinically representative conditions using non-participating observer ratings. Results demonstrate that CBT group therapists use more cognitive, behavioural and psychoeducational strategies, foster self-efficacy to a larger extent and are more supporting and empathetic. PDT group therapists use more interpretative and confrontative interventions and focus on interactional and dynamic aspects. The results strongly support that not only in individual psychotherapy-as shown in prior research-but also in the group setting do CBT and PDT reveal very distinct profiles and that therapists primarily abide by their theoretical training also in clinical practice. They allow one to identify differential process components of the group setting and to trace back parameters of outcome to the process of CBT and PDT for clinical routines. 2008 John Wiley & Sons, Ltd.