Web-based parenting interventions have the potential to increase the currently low reach of parenting programs, but few evidence-based online programs are available, and little is known about who benefits from this delivery format. This study investigated if improvements in child behavior and parenting, following participation in a brief online parenting program (Triple P Online Brief), can be predicted by family and program-related factors. Participants were 100 parents of 2-9-year-old children displaying disruptive behavior problems. Regression analyses showed that higher baseline levels of child behavior problems, older parental age and more intense conflict over parenting pre-intervention predicted greater improvement in child behavior at 9-month follow-up. Improvement in parenting was predicted by higher pre-intervention levels of ineffective parenting. Family demographics, parental adjustment and program related factors did not predict treatment outcomes. Younger child age and lower disagreement over parenting pre-intervention predicted completion of the recommended minimum dose of the program.