Improving and maintaining quality in ethnicity data collections in the health and disability sector was produced as part of a broader project funded by Te Kete Hauora, Ministry of Health to investigate issues with ethnicity data in New Zealand and the implications of these for the Māori health and disability sector. The paper is one in a series of topic-based discussion papers. It considers what is currently known about the state of ethnicity data across the health and disability sector. It also describes key activities to improve and maintain ethnicity data in the health system in New Zealand, and identifies barriers and facilitators to the collection of ethnicity data and the maintenance of high quality datasets. The paper aims to summarise key issues in order to support data collection policies and practices going forward.