In 2003, the program "The combined DAK therapy of obesity for children and adolescents", funded and conducted by the Deutsche Angestellten Krankenkasse (DAK) (A German Health Insurance Company), has started. The whole treatment lasts for 1 year including an initial inpatient therapy for 6 weeks followed by an outpatient treatment at home that adresses the overweight patients and their families. The therapy contents are developed according to the recommendations of the "Arbeitsgemeinschaft Adipositas im Kindes- und Jugendalter (AGA)". In a prospective cohort study a sample of 604 subjects was studied in order to examine the achievement of the treatment goals weight reduction, behaviour modification and improvement of quality of life. The development of weight was evaluated using BMI-SDS. 44,1% of children and adolescents had a successful weight reduction, they reduced their weight at least by 0,3 BMI-SDS. Furthermore, significant changes of health behaviour, physical fitness and quality of life were observed. However, during the outpatient treatment an impairment of some behaviour changes were observed. Nevertheless, the study has identified significant, positive effects in weight loss, behaviour modifications, changes in physical fitness and in the development of quality of life as a result of the therapy. It is demonstrated that a relapse in "old behaviour" followed by an increase of weight after the inpatient treatment can be avoided bythe subsequent outpatient therapy.