Relatively little is known about those who cyberbully others, especially in a UK context. We drew on data from 1144 young people aged 12-13 in eight English secondary schools to examine the prevalence of cyberbullying perpetration and its associations with sociodemographics, other behaviours, and health outcomes. Overall, 14.1% of respondents reported ever cyberbullying others with no significant differences by gender or socioeconomic status. Drawing on mixed-effects logistic regression models, first we found a strong, dose-response relationship between aggressive behaviour at school and cyberbullying others, suggesting that cyberbullying may not only be a facet of wider patterns of bullying but also of aggression more broadly. Second, cyberbullying others was associated with poorer quality of life and with psychological difficulties but not with peer/social problems or worse mental wellbeing. Longitudinal studies are needed to assess whether such associations are causal.