Objective: Attention-deficit/hyperactivity disorder (ADHD) is associated with significant challenges in child functioning. Although behavioral parent training (BPT) can reduce ADHD symptoms, factors associated with traditional face-to-face (F2F) delivery results in only about half of families receiving BPT. The purpose of this pilot randomized controlled trial was to examine parent engagement and program acceptability of F2F and online BPT as well as the efficacy of both formats relative to a waitlist control (WLC) group. Method: Participants were 47 families with preschool children (30 boys, 17 girls) who were between the ages of 3-0 to 5-11 years old who were identified at-risk for ADHD. Children were randomly assigned to F2F or online BPT or to WLC; parents in the two treatment conditions received 10 sessions of BPT. Assessment data for all groups were collected at pre-, mid-, and post-treatment. Results: Both intervention formats resulted in high attendance (M=80%), significantly improved parent knowledge of interventions, treatment implementation fidelity, and child behavior (reduced restlessness and impulsivity, improved self-control, affect, and mood) compared with WLC. However, parents in the F2F group reported significantly higher acceptability ratings than parents in the online group. Conclusions: Findings indicate a streamlined BPT delivered online or F2F results in high levels of engagement, acceptability, as well as parent treatment knowledge and fidelity. Online BPT is associated with similar efficacious outcomes with F2F BPT, suggesting the need for further research to determine variables that predict greater acceptability for and adoption of this format. [This paper was published in "Journal of Clinical Child and Adolescent Psychology" v47 suppl 1 pS369-S383 2018.]