Background: While empirical testing of many of the interRAI Child and Youth Mental Health (ChYMH) assessment scales have been found to be reliable and valid across both child and adult samples, other scales have yet to be psychometrically evaluated within child populations. Objective: The current study evaluates the psychometric properties of the Depressive Severity Index (DSI) embedded in the ChYMH instrument in a child sample. Method: ChYMH data from 6093 children (aged 4-18) across mental health agencies in Ontario, Canada, were obtained. Results: The scale showed good inter-item reliability with a Cronbach's alpha of 0.86 and high inter-item correlations. The scale also demonstrated good convergent validity when tested against DSM-IV mood disorders diagnosis, Child Behaviour Checklist Internalizing scores, and Behaviour Assessment System for Children, Third Edition-Depression scores. Furthermore, children's DSI scores significantly predicted their s-injury attempts and suicide intent using receiver operating characteristic (ROC) analysis, showing good criterion validity of the scale. Conclusions: Overall, the results were in support of the reliability, convergent validity, and criterion validity of the DSI in detecting depression symptoms in the children and youth population.