Using a subsample of 105 children and their parents (100 mothers, 57 fathers) from the Multimodal Treatment Study of Children with ADHD (the MTA), the value of parents' baseline cognitions as predictors of children's treatment outcome at 14 months was examined. Measures of parents' cognitions about themselves, their ADHD children, and their parenting, as well as a self-report measure of dysfunctional discipline were included. Both mothers' and fathers' self-reported use of dysfunctional discipline predicted worse child treatment outcome. Low self-esteem in mothers, low parenting efficacy in fathers, and fathers' attributions of noncompliance to their ADHD child's insufficient effort and bad mood also were associated with worse child treatment outcome. All of these predictive relations were obtained even after MTA treatment effects had been taken into account. Secondary analyses indicated that mothers had a more external locus of control, lower self-esteem, lower parenting efficacy, and a greater tendency to attribute noncompliance to their ADHD child's bad mood than did fathers.