Objective: To examine trends in reports of child maltreatment to the Northern Territory Department of Children and Families among Aboriginal and non-Aboriginal children. Design, setting and subjects: A historical cohort study using administrative data collections of notifications and substantiated cases of maltreatment among children aged from 0 to 17 years. Main outcome measures: Annual rates of notification and substantiation of different types of child maltreatment. Results: From 1999 to 2010, the overall annual rates of notification for maltreatment of Aboriginal children showed an average increase of 21% (incidence rate ratio [IRR], 1.21; 95% CI, 1.19–1.24). The greatest increases were in notifications for neglect and emotional abuse. There were parallel increases in rates of substantiated cases of maltreatment. Among non-Aboriginal children, the overall annual rates of notification also increased (IRR, 1.10; 95% CI, 1.07–1.14); however, changes in annual rates of substantiated cases for all types of maltreatment were not statistically significant. Conclusion: There have been considerable increases in both notifications and substantiated cases of child maltreatment, most prominently among Aboriginal children. It is possible that the observed increases reflect increasing incidence of maltreatment; however, they are also consistent with a mix of increased surveillance, improved service access, changes in policy and a shift in public attitudes.