IntroductionChildren and adolescents with overweight and obesity have an impaired health-related quality of life (HRQoL). However, it is unclear which of these children are most affected in their physical, psychological, and social functioning. Therefore, this study aimed to evaluate HRQoL in treatment-seeking children and adolescents with overweight, obesity, and severe obesity.MethodsA cross-sectional study was performed at the Centre for Overweight Adolescent and Children's Healthcare (COACH). Children and adolescents (8–17 years) with overweight, obesity, and severe obesity were included. The primary outcome was the self-reported HRQoL measured with the KIDSCREEN-27.ResultsA total of 419 participants with overweight (N= 121), obesity (N= 182), and severe obesity (N= 116) were included. One-way ANOVA analysis showed that children and adolescents with severe obesity reported significantly lower physical well-being (41.25 ± 13.14) compared to those with overweight (47.91 ± 12.53;p< 0.001) and obesity (46.74 ± 11.93;p< 0.001). Furthermore, impaired psychological well-being was found in the group with severe obesity (45.14 ± 13.27) in comparison to the group with overweight (50.90 ± 9.48;p< 0.001) and obesity (49.71 ± 10.95;p= 0.002). Multivariable linear regression analysis, while correcting for age, sex, cardio metabolic health risk, and ethnicity, revealed similar results. Additionally, children and adolescents with severe obesity scored lower regarding autonomy and parent relation than those with overweight (B= 3.95;p= 0.009). In almost all groups and dimensions of the KIDSCREEN-27, caregivers scored lower compared to the children and adolescents themselves. Furthermore, a low child-caregiver agreement seemed to exist, especially in the children and adolescents with overweight.ConclusionThe HRQoL of treatment-seeking children and adolescents with overweight and obesity was most affected in children and adolescents with the most severe grade of obesity. Following these findings, lifestyle intervention programs targeting childhood obesity should be aware of this even more vulnerable group so that treatments can be tailored according to their needs.