AIMS/HYPOTHESIS: Large-scale data on age- and sex-specific dementia mortality trends among people with diabetes remain limited, as most previous studies have been restricted to single countries or have not distinguished mortality by diabetes status. We estimated age- and sex-specific time trends in dementia mortality among individuals with and without diabetes from high-income jurisdictions. METHODS: We analysed aggregated mortality and demographic data using registries and administrative sources in Australia, Canada (Alberta and Ontario), France, Denmark, Finland and Scotland from 2000 to 2023. Poisson regression was used to estimate mortality rates for dementia as the underlying cause of death in people with and without diabetes at 60, 70, 80 and 90 years of age. RESULTS: A total of 114,559 and 589,706 dementia deaths were identified in over 42 and 244 million person-years of follow-up for individuals with and without diagnosed diabetes, respectively. Dementia mortality trends varied by age and jurisdiction but were generally consistent for both sexes. At younger ages (e.g. 60 and 70 years), the dementia mortality trends did not suggest any meaningful increases or decreases, except for in Scotland, which reported increasing dementia mortality over time only for those with diabetes. At older ages (e.g. 80 and 90 years), however, increases in dementia mortality were observed in most jurisdictions, ranging from 7.6% to 42.4% per 5 years. The magnitude of the increases was generally greater for those with diabetes. Mortality from dementia subtypes (e.g. Alzheimer's disease and vascular dementia) also increased over time in individuals aged 40-89 years, with greater increases in mortality rates for individuals with diabetes, specifically in Australia and Scotland. CONCLUSIONS/INTERPRETATION: Increases in dementia mortality were observed for those aged 80 years and above and were most marked for people with diabetes. These findings highlight the growing burden of dementia for health systems.