Having an effective triage tool is an important step toward a careful use of the restricted time and qualified personnel to perform comprehensive psychiatric assessment in juvenile justice settings. The aims of this study were to examine the construct validity of the Massachusetts Youth Screening Inventory—second version (MAYSI-2), and its likelihood to identify youths who might have a psychiatric disorder. Data from up to 781 male adolescents (mean age = 16.73 years) were gathered as part of the standardized mental health screening and assessment in two all-male Youth Detention Centers in the Netherlands. Categorical assessments were based on two structured diagnostic interviews. Sensitivity, specificity, positive and negative predictive values, and the area under the curve were calculated to evaluate the likelihood of the MAYSI-2 to identify youths with a psychiatric disorder. Youths with a disorder scored significantly higher on the corresponding MAYSI-2 subscale than youths without a disorder. In the total sample, 70 % of the youths with a disorder met the Caution cut-off criteria on at least one MAYSI-2 scale, while youths without a psychiatric disorder were very unlikely to meet cut-off criteria for multiple MAYSI-2 scales. Overall, the sensitivity was slightly better when analyses were repeated in groups of youths from various ethnic origins. The findings supported the construct validity of the Dutch MAYSI-2 and suggested that the MAYSI-2 is a valid mental health screening tool that may serve relatively well as a triage tool. Its effectiveness, however, may differ between ethnic groups.