Abstract: There has been no published research to date specifically on young people who sexually abuse in both family and community settings. This exploratory study looked at 34 young people displaying harmful sexual behaviour, and found that abusive sexual behaviour progressed from the family into the community, rather than the other way around. Boys whose abuse took place within both the family and the community were more likely to have a younger age of onset of abusive behaviour and to have experienced more abuse themselves. Boys whose abuse of their siblings was motivated substantially by jealous anger were less likely to go on to abuse outside their family. This may suggest a different dynamic and pathway for boys who abuse only siblings, and that sibling sexual abuse is a useful concept to describe a particular subset of young people who display harmful sexual behaviours.