Psychological functioning can be adversely impacted after a mild traumatic brain injury (mTBI) and may be a potential target for intervention. Despite the use of symptom ratings or structured diagnostic interview to assess long-term anxiety and depression symptoms in children and adolescents post-injury, no known studies have considered the agreement between different assessment methods and between respondents. The objectives of this study were to investigate the agreement between symptom ratings and structured diagnostic interview and between children and parents' symptom reporting. Participants (N = 33; 9-18 years old) were recruited from the Emergency Department and assessed on average 22.8 months (SD = 5.6) after their mTBI. Anxiety and depression symptoms were evaluated via subscales of a questionnaire (Behavior Assessment System for Children) and parts of a computerized structured diagnostic interview (generalized anxiety disorder and major depressive episode; Diagnostic Interview Schedule for Children - C-DISC-IV) administered individually to children and their parents. Results showed that the inter-method agreement to identify high levels of anxiety and depression was moderate to perfect in children while it was lower in parents. Although a similar percentage of participants with elevated anxiety or depression were identified by both children and parents, the agreement between youth and parents was variable, ranging from poor to good for anxiety and poor to moderate for depression. These results highlight the importance of collecting youth and parents' reports of anxiety and depression symptoms and considering potential discrepancies between informants' answers.