Recent studies on the treatment of overweight and obesity in children and adolescents have generally considered single psychological or somatic parameters. The present study examined the efficacy of multimodal obesity treatment in routine care in N=278 children and adolescents (ages 2-17) over 12 months using comprehensive psychological and somatic parameters. The primary endpoint was the objectively measured change of BMI-SDS (Body Mass Index Standard Deviation Score). Secondary objectives included patient-reported health-related quality of life, general and eating disorder psychopathology, weight-related self-stigmatization as well as objectively measured parameters of lipoprotein and glucose metabolism and liver enzymes. At the end of treatment after 12 months, there was significant improvement in BMI-SDS (M=-0.10; SD=0.32) and single liver enzymes in the total sample whereas psychological and other blood parameters showed no significant improvement. Treatment responders showed greater BMI-SDS reductions (M=-0.44; SD=0.22) as well as similar results concerning blood and psychological parameters compared to the total sample. This multimodal obesity treatment in routine care mostly improved patients' BMI-SDS and single somatic parameters, but not psychological parameters. Patients' psychological stressors emphasize the need for psychotherapeutic treatment going beyond reduction of BMI-SDS. Furthermore, these results underline the importance of comprehensive evaluation of psychological and somatic parameters to improve treatment outcome.