BackgroundIn England, a third of emergency admissions of adolescents for injury are adversity related (violent, self-inflicted, drug-related, or alcohol-related). A comparison of time trends of the incidence of admissions for violent injury between England and Scotland revealed steeper declines in 2005–11 in Scotland. We aimed to determine whether incidence of admissions for any adversity-related injury varied substantially between the two countries. MethodsWe conducted time-series analyses of emergency admissions between 2005 and 2011 for adversity-related injury (defined by the 10th revision of the International Classification of Diseases) to National Health Service hospitals in England (Hospital Episode Statistics) and in Scotland (Scottish Morbidity Records) in 10–18 year olds. Analyses were stratified in groups by sex and age (10–12 years, 13–15, 16–18) and were adjusted for background trends in admissions for any injury. FindingsIn 2005, rates of admissions per 100 000 for adversity-related injury ranged from 48·9 for girls aged 10–12 years in Scotland (95% CI 0–98·9) to 978·2 for boys aged 16–18 years in Scotland (764·0–1184·3). Rates for 10–12-year-old girls and boys, respectively, were similar between the two countries, but were higher in Scotland for 13–15 year olds and 16–18 year olds. From 2005 to 2011, rates decreased in both countries for all groups by −1·5% per year (95% CI −3·2 to 0·21) to −10·0% per year (–15·2 to −4·4), except for 16–18-year-old girls and boys in England, where rates increased by 0·25% per year (0·09–0·41) to 2·5% per year (1·2–3·7). Decreases in all groups were greater in Scotland than in England after adjustment for trends in admissions for any injury. By 2011, although incidences of admissions for adversity-related injury in adolescents aged 13–15 and 16–18 years remained higher in Scotland, differences between England and Scotland were smaller than in 2005. InterpretationOur finding that rates of admissions for adversity-related injury decreased more steeply in Scotland than in England raises questions about the factors driving these discrepancies. Several initiatives within each country might have been influential. For example, the English government attempted to tackle incidence of violence and gangs by targeting high crime areas with higher levels of policing. The Scottish government set up contracts with local gangs to exchange a so-called clean slate for psychosocial support. Further research into potentially successful practices in Scotland could be used to develop future initiatives to reduce harm in adolescents in both countries and further afield. More research is needed, especially into why the incidence of admissions for adversity-related injury increased for older adolescents in England. FundingAH was supported by the Policy Research Unit in the Health of Children, Young People and Families, which is funded by the Department of Health Policy Research Programme (grant reference number 109/0001). AH is also supported by the University College London Impact studentship. The study sponsors played no part in the design, data analysis, and interpretation of this study; the writing of the abstract; or the decision to submit the abstract for publication.