ObjectiveTo investigate the association of mental health in childhood and adolescence with four outcomes at 18y: ultra-processed food (UPF) consumption, body mass index (BMI), excessive weight (EW), and body composition, including fat mass (FM) and fat free mass (FFM) in kg, FM index (FMI) and FFM index (FFMI) in kg/m2. Research Methods & ProceduresCohort study in which The Development and Well-Being Assessment (DAWBA) (6 and 11y) and the MINI International Neuropsychiatric Interview (MINI) (18y) provided information on internalizing (INT), externalizing (EXT) and any mental disorder (ANY). The exposure was classified in: “never”, “at 6 and/or 11y”, “at 18y only” and “at 6, 11 and 18y”. Linear and logistic regression were run. All analyses were stratified by sex. Results2,722 participants were analyzed. At 18y, female with EXT disorders at 6 and/or 11y presented higher BMI (β: 1.70; 0.18-3.23), FM (β: 4.74; 1.42-8.06), and FMI (β: 1.53; 0.28-2.79) than those who never had. The odds of EW at 18y was also higher in females with EXT disorders at 6 and/or 11y (OR: 3.39; 1.56-7.36) and at the three time points (OR: 7.08; 1.69-29.59). Males with EXT disorders at 6 and/or 11y presented higher FM (β: 4.45; 1.85-7.06) and FMI (β: 1.47; 0.63-2.31). ConclusionAmong children and adolescents showing symptoms of EXT disorders, weight should be monitored carefully, thus ultimately contributing to reduce the burden of EW in adolescence.