The present study focuses on the validity of questionnaire self-report of psychopathology and parent-child relationship quality for juvenile delinquents with severe behavioural and psychiatric disorders by comparing information derived from questionnaire self-report with information from other sources, including parent report, in-depth interviewing, behavioural observation by clinicians, and official criminal records. The sample consisted of N=33 juvenile delinquents with psychiatric disorders. The juvenile delinquents did not report increased levels of psychopathology or poor relationships with their parents, which is inconsistent with the fact that all juvenile delinquents were in day treatment for severe behavioural maladaptation and relationship problems. Moreover, parent ratings of psychopathology were consistently in the clinical range and relationship quality was evaluated as very poor by the parents (d>.80). We conclude that screening instruments for psychopathology and assessment of relationship quality relying on questionnaire self-report may not yield valid scores in this (extreme) population of juvenile delinquents.