Adolescent poor sleep is common and has been associated with unintentional injury risks. Yet the comparability of evidence is limited by differences in measures of sleep and injury implemented across studies. We examined the potential cross-national consistency of relationships between poor sleep and unintentional injury using self-reports from 239 816 adolescents (50.8% girls) in 46 countries collected using a common survey procedure. A cross-sectional study was conducted using nationally representative records from the 2017/2018 International Health Behaviour in School-aged Children study. The prevalence of sleep indicators (difficulties in falling asleep, insufficient sleep, social jetlag) and annual medically treated injuries (any, multiple) were described cross-nationally and by gender. Multivariable modified Poisson regression analyses were conducted within and across countries to test the consistency of associations between sleep and injury. 16.3%-48.3% of adolescents reported an indicator of poor sleep and 44.0% sustained any injury. We observed striking cross-national variations in sleep, yet consistent gendered patterns across countries [e.g. sleep difficulties more prevalent among girls vs. insufficient sleep (non-school days) more prevalent among boys]. Country-level models displayed relatively consistent and positive associations. Multi-country (pooled) models demonstrated a consistency of effects, with the strongest association observed between difficulties in falling asleep and multiple injuries (prevalence ratio: 1.58, 95% CI: 1.55-1.61); these effects were especially pronounced in girls. Using standard indicators, this novel cross-national study demonstrated that poor sleep is a consistent risk factor for adolescent injuries. Given the recent epidemic of adolescent sleep problems, sleep hygiene represents a novel target for injury prevention.