Objective: To examine the contribution of parent report to youth report in defining psychiatric "caseness" among incarcerated youths. The authors compared reports with each other and examined the influence of varying case definitions. Method: A total of 569 youths in New Jersey, Illinois, and South Carolina admitted into secure placement from 1999 to 2002 were self-administered the Diagnostic Interview Schedule for Children Version 4 (DISC-IV). Parents of assessed youths were asked to complete a parent version of the DISC-IV by telephone. This paper reports on 122 youth-parent dyads. Results: There were four major findings: (1) youths report higher rates of disorder than parents, with rates decreasing when agreement between parents AND youths is required and increasing when parent OR youth report is required; (2) parents and youths showed significant agreement on reports of lifetime suicide attempt; (3) parents were more likely than youths to report that disorders were impairing; and (4) only 30% of parents added substantial new information to the youth report. Conclusions: Parent report potentially adds new information for youths who do not endorse any impairment or deny disorder. However, the value of including parent report for youths in justice and other under-resourced, settings should be balanced with the real challenges involved in obtaining information from parents.