Objective: This randomized controlled trial examined the efficacy of Triple P Online Brief, a low-intensity online positive parenting program for parents of children with early onset disruptive behavior problems. Method: Two hundred parents with 2-9-year-old children displaying early onset disruptive behavior difficulties were randomly assigned to either the intervention condition (n = 100) or a Waitlist Control group (n = 100). Results: At 8-week post-assessment, parents in the intervention group displayed significantly less use of ineffective parenting strategies and significantly more confidence in dealing with a range of behavior concerns. These effects were maintained at 9-month follow-up assessment. A delayed effect was found for child behavior problems, with parents in the intervention group reporting significantly fewer and less frequent child behavior problems at follow-up, but not at post-assessment. All effect sizes were in the small to medium range. There were no significant improvements in observed negative parent and child behavior. No change was seen for parents’ adjustment, anger, or conflict over parenting. Consumer satisfaction ratings for the program were high. Conclusions: A brief, low-intensity parenting program delivered via the Internet can bring about significant improvements in parenting and child behavior.