Objective: To explore the significance of adding father ratings to mother and teacher ratings in the assessment of ADHD symptoms in children. Method: The ADHD Rating Scale–IV, the Child Behavior Checklist, and the Teacher Report Form were filled out by all three informants for a sample of 48 clinically referred children (79% boys) aged 6 to 15 (M = 10.1) years. Results: Correspondence between father and teacher reports on ADHD-specific symptoms (intraclass correlation coefficient [ICC] = .38) exceeded that between mothers and teachers (ICC = .23). Fathers rated their children as having fewer problems than did mothers and teachers on Total scale scores and the Inattention subscale of the ADHD Rating Scale–IV. Mother ratings were more sensitive to an ADHD diagnosis, whereas father ratings better predicted an ADHD diagnosis requiring the two-setting criterion. Conclusion: The choice of parent informant and informant combination had a considerable impact on parent–teacher concordance and estimates of ADHD symptoms and subtypes in the child. (J. of Att. Dis. 2012; XX(X) 1-XX)