There is limited research on the psychosocial health of Asian adolescents undergoing obesity treatment. Our study examined the predictors of psychological distress, disordered eating and poor health-related quality of life (HRQoL) in these adolescents and the associations between them. A total of 82 adolescents aged 11-17 years were recruited from the Weight Management Clinic in KK Women's and Children's Hospital between June 2022 and January 2023. Participants completed the following questionnaires: (a) Young Person's Clinical Outcomes in Routine Evaluation (YP-Core) assessing for psychological distress, (b) Children's Eating Attitude Test (ChEAT) evaluating for disordered eating behaviours, and (c) Pediatric Quality of Life Inventory (PedsQL) measuring HRQoL. Participating adolescents had a mean body mass index of 31.9 ± 5.1 kg/m2. Of the participants, 40% reported significantly symptomatic psychological distress (YP-Core score ≥14) and 16% were at risk of eating disorders (ChEAT score ≥20). A higher YP-Core score was the only significant determinant of poorer HRQoL, after controlling for demographic variables and ChEAT scores. Malay (regression coefficient: 6.6, 95% confidence interval [CI]: 0.6-12.6, P = 0.031) and Indian (regression coefficient: 8.9, 95% CI: 3.8-14.0, P = 0.001) adolescents were more likely to report disordered eating and psychological distress, respectively, as compared to Chinese adolescents. Adolescents whose parent(s) had obesity (regression coefficient: 3.4, 95% CI: 0.1-6.7, P = 0.043) were also more likely to experience greater psychological distress. Understanding the determinants of psychological distress, disordered eating and HRQoL will facilitate targeted screening and management of the psychosocial complications of adolescent obesity.