In order to evaluate the effectiveness of a cognitive behavioural group therapy programme for the treatment of obesity in clinical practice, 122 patients from 14 general practices (n = 70) were randomised into either a treatment or a control arm with a ratio of 3 to 2. The group treatment programme was also assessed in a clinical centre (n = 52; University Hospital Basel). Before therapy, a clinical interview and a mental disorder examination were carried out on all patients. The instructors of the programme (practitioners; clinic physicians) were trained during two afternoon meetings to supervise the group sessions. The treatment programme consisted of 16 group sessions of 90 min each, and contained psycho-educational elements concerning a balanced diet, instruction for the integration of more activity in everyday life (lifestyle activity), problemsolving strategies, and the cognitive restructuring of dysfunctional cognition regarding the own body. All the patients who were treated in the various settings demonstrated a benefit from therapy. Compared to the control groups which received usual medical care, they were able to reduce their starting weight by around 5% (p <0.001 for the group treated by practitioners) at the end of treatment and stabilise it until follow up after one year. In regard to psychological factors the treatment groups showed an increased sense of control over eating behaviour, and feelings of distractibility and hunger were reduced after treatment and at follow up (p <0.05). All treatment groups showed statistically relevant increases in feelings of attractiveness regarding their body and shape (p <0.05). These results support the effectiveness of the integrated cognitive behavioural treatment programme in clinical practice over a duration of 12 months.