Objective: This study was conducted to assess treatment decision-making capacity (TDMC) in a child and adolescent psychiatric sample and to verify possible associations between TDMC, psychiatric symptom severity, and cognitive functioning.Methods: Twenty-two consecutively recruited patients hospitalized for an acute mental disorder, aged 11–18 years, underwent measurement of TDMC by the MacArthur Competence Assessment Tool for Treatment (MacCAT-T). The MacCAT-T interview focused on patients' current treatment, which comprised second-generation antipsychotics (45.5%), first-generation antipsychotics (13.6%), antiepileptic drugs used as mood stabilizers or lithium carbonate (45.5%), selective serotonin reuptake inhibitors (32%), and benzodiazepines (18%). We moreover measured cognitive functioning (Wechsler Intelligence Scale for Children III) and psychiatric symptom severity (Brief Psychiatric Rating Scale v 4.0).Results: Patients' TDMC varied within the sample, but MacCAT-T scores were good in the sample overall, suggesting that children and adolescents with severe mental disorders could be competent to consent to treatment. The TDMC proved independent of psychiatric diagnosis while being positively associated with cognitive functioning and negatively with excitement.Conclusion: The MacCAT-T proved feasible for measuring TDMC in a child and adolescent psychiatric sample. TDMC in minors with severe mental disorders was not necessarily impaired. These results deserve reconsidering the interplay between minors and surrogate decision-makers as concerning treatment decisions.