The five participating university centers are distributed across 4 geographic regions in the North (Berlin), in the West (Essen/Datteln), in the East (Leipzig) and in the South (Ulm) of Germany, and will therefore render data that are representative of Germany as a whole. We will screen a 600 adolescents age 14 to 24.9 years (initially up to 21 years; this was changed in an amendment in February 2013) with extreme obesity (BMI ≥ 35 kg/m2) and 600 adolescents with obesity (BMI 30-34.9 kg/m2) over a 24 months period. A total of 350 subjects will be enrolled. Baseline assessments include an array of standardized questionnaires and validated instruments to assess health, psycho-social situation, psychiatric co-morbidities and health related quality of life, as well as an in-depth medical evaluation. Individuals who complete the baseline evaluations will be invited to participate in 6 group sessions over a 3 months period. Group assignment to the low key intervention vs. standard care group will be at random. The effects of the interventions on health related quality of life and psycho-social functioning will be assessed via questionnaires after 6 months. Subsequently, subjects will be invited to participate in additional components of YES.