Objective: To describe health-related quality of life (HRQOL) and psychological well-being of children and adolescents at enrolment in a multidisciplinary community-based obesity programme and to determine association with ethnicity. This programme targeted indigenous people and those from most deprived households. Further, this cohort was compared with other populations/normative data. Methods: This study examines baseline demographic data of an unblinded randomised controlled clinical trial. Participants (recruited from January 2012-August 2014) resided in Taranaki, New Zealand, and for this study we only included those with a body mass index (BMI) ≥98th percentile (obese). HRQOL and psychological well-being were assessed using the Pediatric Quality of Life Inventory (PedsQL V.4.0) (parent and child reports), and Achenbach's Child Behavior Checklist (CBCL)/Youth Self Report (YSR).Results: Assessments were undertaken for 233 participants (45% Māori, 45% New Zealand European, 10% other ethnicities, 52% female, 30% from the most deprived household quintile), mean age 10.6 years. The mean BMI SD score (SDS) was 3.12 (range 2.01-5.34). Total PedsQL generic scaled score (parent) was lower (mean=63.4, SD 14.0) than an age-matched group of Australian children without obesity from the Health of Young Victorians study (mean=83.1, SD 12.5). In multivariable models, child and parental generic scaled scores decreased in older children (β=-0.70 and p=0.031, β=-0.64 and p=0.047, respectively). Behavioural difficulties (CBCL/YSR total score) were reported in 43.5% of participants, with the rate of emotional/behavioural difficulties six times higher than reported norms (p