Background: The program The combined DAK therapy for obesity in children and adolescents’ funded and conducted by the Deutsche Angestellten-Krankenkasse (DAK), a German health insurance company, commenced in 2003. The treatment program lasts for 1 year and comprises of 2 phases: an initial inpatient therapy for 6 weeks followed by a home-based outpatient treatment of the overweight children, adolescents, and their families for 10.5 months. The therapy complies with the guidelines of the German Working Group of Obesity in Childhood and Adolescence (AGA). Participants and Methods: In this study, 162 obese children and adolescents were compared with a control group of 75 obese subjects recruited from the waiting list for the program. The aim was to analyze whether the changes in weight, eating behavior, and physical fitness during the therapy period are a result of the therapy itself or whether they are attributable to external effects. Body weight, height, and physical fitness were assessed through direct measurements while behavior and quality of life were assessed using self-report questionnaires. The development of body weight was evaluated using the BMI-SDS which is a measure of how many standard deviations an individual BMI is above or below the age- and gender-specific mean. Results: Within the observation period the BMISDS decreased significantly by 0.36 ± 0.34 in the intervention group, whereas no changes of BMI-SDS were observed in the control group (0.04 ± 0.17). The study revealed significant, positive treatment effects in exploratory analyses with regard to weight loss, behavior changes, physical fitness, and development of quality of life as a result of the therapy. These effects were not seen in the control group. Conclusion: We conclude that these positive developments are a result of the treatment program.