This study aims to explore the influence of paternal variables on outcome of behavioral parent training (BPT) in children with attention-deficit/hyperactivity disorder (ADHD). 83 referred, school-aged children with ADHD were randomly assigned to BPT plus ongoing routine clinical care (RCC) or RCC alone. Treatment outcome was based on parent-reported ADHD symptoms and behavioral problems. Moderator variables included paternal ADHD symptoms, depressive symptoms, and parenting self-efficacy. We conducted repeated measures analyses of variance (ANOVA) for all variables, and then analyzed the direction of interaction effects by repeated measures ANOVA in high and low scoring subgroups. Paternal ADHD symptoms and parenting self-efficacy played a moderating role in decreasing behavioral problems, but not in decreasing ADHD symptoms. Paternal depressive symptoms did not moderate either treatment outcome. BPT is most beneficial in reducing children’s behavioral problems when their fathers have high levels of ADHD symptoms or high-parenting self-efficacy.