Given the high overweight prevalence among children with a migration background in Germany, this paper describes barriers to the treatment of paediatric obesity in a specialized clinic providing services to an ethnically diverse population. In a cross-sectional mixed-method design, a two-week participant observation was followed by a cultural competence survey among the healthcare professionals employed at the clinic. The present study revealed barriers related to all categories of social actors involved in the therapy process. A major difficulty encountered by providers when working with ethnically diverse patients was the lack of mutual understanding, often associated with language barriers. Language barriers were most prevalent between providers and ethnically diverse mothers. Targeted education programs for adults (particularly women) with a migration background and cultural competence training for healthcare providers are needed in Germany. Special attention should be paid to scheduling appointments and enhancing patients' engagement in the therapy process.