To date, research focused on ''traditional'' (i.e. in-person) youth bullying behaviour has documented serious psychosocial challenges for those involved. How this literature translates to youth engaging in aggressive behaviours online has yet to be examined. Using the largest US sample of youth Internet users to date, psychosocial characteristics of youth engaging in Internet harassment were examined. Results from the nationally representative survey suggested that Internet harassment is a significant public health issue, with aggressors facing multiple psychosocial challenges including poor parent-child relationships, substance use, and delinquency. Comparisons to traditional bullies were made, with similarities and differences noted.