Introduction: A National Diabetes Register was established in the National Board of Health in 2006 following a pilot study showing the feasibility of doing so based on existing registers. Content: The register contains data of birth, date of inclusion, and date of death as well as information on the criteria met for inclusion. Validity and coverage: The register is more than 90% complete when compared to records of general practitioners, and it covers the entire Danish population. Conclusion: The register is a source of demographic information for the diabetes population in itself, but also a source of linkable information for studies of diabetes as outcome and as determinant.