To describe the psychometric properties of the Strengths and Difficulties Questionnaire (SDQ), a brief measure of the prosocial behavior and psychopathology of 3-16-year-olds that can be completed by parents, teachers, or youths. A nationwide epidemiological sample of 10,438 British 5-15-year-olds obtained SDQs from 96% of parents, 70% of teachers, and 91% of 11-15-year-olds. Blind to the SDQ findings, all subjects were also assigned DSM-IVdiagnoses based on a clinical review of detailed interview measures. The predicted five-factor structure (emotional, conduct, hyperactivity-inattention, peer, prosocial) was confirmed. Internalizing and externalizing scales were relatively "uncontaminated" by one another. Reliability was generally satisfactory, whether judged by internal consistency (mean Cronbach a: .73), cross-informant correlation (mean: 0.34), or retest stability after 4 to 6 months (mean: 0.62). SDQ scores above the 90th percentile predicted a substantially raised probability of independently diagnosed psychiatric disorders (mean odds ratio: 15.7 for parent scales, 15.2 for teacher scales, 6.2 for youth scales). The reliability and validity of the SDQ make it a useful brief measure of the adjustment and psychopathology of children and adolescents.