IntroductionThere are no national dementia epidemiological studies using New Zealand (NZ) data. NZ routinely collects healthcare data within the Integrated Data Infrastructure (IDI). Late-onset dementia estimates were investigated using the IDI, 2012-2015; and compared with published estimates; variations between North and South Islands, and ethnicity.MethodsA population-based, retrospective cohort design was applied to routinely-collected de-identified health/administrative IDI data. Dementia was defined by ICD-10-AM dementia codes or anti-dementia drugs. ResultsApproximately 2% of >60 year old population had dementia, lower than published estimates. Dementia was higher in North Island; 80-89 year olds; in Māori population when age-standardised; and 9% had >1 dementia sub-type. Conclusions To our knowledge, this is the first study ascertaining dementia estimates using NZ’s whole-of-population IDI data. Estimates were lower than existing NZ estimates, for several reasons. Further work is required, including expanding IDI datasets, to develop future estimates that better reflect NZ’s diverse population.