This report describes improvements to case ascertainment for the National Diabetes Register (NDR). The NDR is a register of people living in Australia with insulin-treated diabetes. The National Diabetes Services Scheme (NDSS) is one of the NDR's main data sources. Recent changes to the NDSS registration form have increased the notification of new cases to the NDR. This information paper describes the phasing-in of the new NDSS registration form and the resulting improvement in ascertainment for the NDR. It also provides information to help users of NDR data to understand the effects of the changed ascertainment so that the data can be appropriately used and interpreted, particularly for comparisons over time. It is therefore a valuable resource for researchers interested in using the NDR.