This study examined the extent to which maternal attention-deficit/hyperactivity disorder (ADHD) symptoms predict improvement in child behavior following brief behavioral parent training. Change in parenting was examined as a potential mediator of the negative relationship between maternal ADHD symptoms and improvement in child behavior. Seventy mothers of 6–10 year old children with ADHD underwent a comprehensive assessment of adult ADHD prior to participating in an abbreviated parent training program. Before and after treatment, parenting was assessed via maternal reports and observations and child disruptive behavior was measured via maternal report. Controlling for pre-treatment levels, maternal ADHD symptomatology predicted post-treatment child disruptive behavior problems. The relation between maternal ADHD symptomatology and improvement in child behavior was mediated by change in observed maternal negative parenting. This study replicated findings linking maternal ADHD symptoms with attenuated child improvement following parent training, and is the first to demonstrate that negative parenting at least partially explains this relationship. Innovative approaches combining evidence-based treatment for adult ADHD with parent training may therefore be necessary for families in which both the mother and child have ADHD. Larger-scale studies using a full evidence-based parent training program are needed to replicate these findings.