The present study examined treatment outcomes for objectively measured parenting behavior in the Multimodal Treatment Study of Children with Attention-Deficit/Hyperactivity Disorder (ADHD). Five hundred seventy-nine ethnically and socioeconomically diverse children with ADHD-combined type (ages 7.0–9.9 years) and their parent(s) were recruited at 6 sites in the United States and Canada and randomly assigned to 1 of 4 treatment groups for 14 months of active intervention: medication management (MedMgt), intensive behavior therapy, combination of the 2 (Comb), or a community-treated comparison (CC). Baseline and posttreatment laboratory observations of parent–child interactions were coded by observers blind to treatment condition. Comb produced significantly greater improvements in constructive parenting than did MedMgt or CC, with effect sizes approaching medium for these contrasts. Treatment effects on child behaviors were not significant. The authors discuss the importance of changes in parenting behavior for families of children with ADHD and the need for reliable and objective measures in evaluating treatment outcome.