In a study of ADHD symptoms in the relatives of probands diagnosed with ADHD, the validity of self-reported and informant-reported symptoms in childhood and adulthood was investigated with a semistructured diagnostic interview, the Schedule for Affective Disorders and Schizophrenia for School-Age Children (K-SADS) adapted for adults, as a criterion. The participating relatives were 80 women and 46 men aged 17 to 77. Rating scales based on the Diagnostic and Statistical Manual of Mental Disorders (4th ed.) were completed by participants and informants. Internal consistency of the scales and interrater reliabilities of the diagnostic interview were satisfactory. Correlations between ratings across sources of information supported convergent and divergent validity. Self-report scales and informant scales predicted interview-based diagnoses in childhood and adulthood with adequate sensitivities and specificities. It was concluded that the rating scales have good psychometric properties, at least in at-risk populations.