Diverse mechanisms account for the familial aggregation of certain personality traits and externalizing psychopathology. We explored the roles of positive and negative parenting as mediators of longitudinal associations between parents' maladaptive personality traits and their children's inattention/hyperactivity problems. We collected self, informant and observational measures of parent personality, parenting and child symptoms from a community sample of 409 children (208 girls) and their primary caregiver across three waves of data collection at child ages 3, 5 and 8 years. Primary caregiver's negative temperament, mistrust and aggression were positively associated with children's symptoms of hyperactivity/inattention. While parenting was unrelated to self-reported traits, responsive parenting mediated negative associations between informant-reported maladaptive parent traits and children's hyperactivity/inattention. In addition, informant-reported trait aggression predicted boys' ADHD symptoms via hostile parenting. Findings implicate mechanisms that may underlie intergenerational transmission and continuity of inattention/hyperactivity and highlight the importance of multi-informant, multi-method approaches when studying relationships between parent traits and child outcomes.