Depression and eating disorders are heightened for adolescents with obesity. Clinical reviews alongside self-report questionnaires are important to ensure appropriate intervention. To evaluate changes in self-report symptoms of depression, eating disorders, and binge eating in adolescents with obesity during the Fast Track to Health trial. This was a randomized clinical trial conducted from 2018 to 2023. It was a multisite trial conducted at children's hospitals in Sydney, New South Wales, and Melbourne, Victoria, Australia, and included adolescents (13-17 years) with obesity (defined as adult equivalent body mass index ≥30; calculated as weight in kilograms divided by height in meters squared) and 1 or more related complications. Duration was 52 weeks including a very low energy diet for 4 weeks followed by intermittent energy restriction (IER) or continuous energy restriction (CER). Self-report symptoms of depression (Center for Epidemiologic Studies Depression Scale-Revised 10-Item Version for Adolescents [CESDR-10]; scores 0-30), eating disorders (Eating Disorder Examination Questionnaire [EDE-Q]; scores 0-6), and binge eating (Binge Eating Scale [BES]; scores 0-46) were assessed. Adolescents were screened for depression and eating disorders (weeks 0, 4, 16, and 52) and monitored for the onset of new symptoms of disordered eating during dietetic consults. Of 141 adolescents (median [IQR] age, 14.8 [12.9-17.9] years; 71 male [50.4%]) enrolled, median baseline EDE-Q score was 2.28 (IQR, 1.43-3.14), median baseline CESDR-10 score was 9.00 (IQR, 4.00-14.50), and median baseline BES score was 11.00 (IQR, 5.00-17.00). There were no differences between groups for change in CESDR-10 (mean difference at week 52, 0.75; 95% CI, -1.86 to 3.37), EDE-Q (mean difference at week 52, 0.02; 95% CI, -0.41 to 0.45), or BES (mean difference at week 52, -2.91; 95% CI, -5.87 to 0.05). The within-group reductions at week 4 were maintained at week 52, for CESDR-10 and EDE-Q, indicating reduced symptoms of depression and eating disorders. Within-group reductions on the BES were maintained in the IER group only. Seventeen adolescents (12.1%) required support or referral for depression and/or disordered eating, including 7 (5%; 5 IER, 2 CER) adolescents who experienced the onset or reemergence of symptoms during the intervention. Results suggest that many treatment-seeking adolescents with obesity self-reported symptoms of depression and eating disorders. Although symptoms reduced for most, some required additional support. Obesity treatment is an opportune time to screen and monitor for depression and disordered eating. Australian New Zealand Clinical Trials Registry: ACTRN12617001630303.