Introduction The global burden of diabetes mellitus (diabetes) is significant and of increasing concern with more pregnant women being diagnosed with gestational diabetes mellitus (GDM). The Cook Islands face mounting pressures to address diabetes alongside competing population health needs and priorities. Cook Islands residents frequently travel to New Zealand to access health services. Inadequate information systems also make it difficult for countries to prioritise preventative measures for investment. In the absence of good data to inform effective diabetes preventative and treatment measures, people with diabetes are likely to progress to complications which will burden society and health systems in the Cook Islands and New Zealand. Aim To determine the prevalence of diabetes and prediabetes, and incidence of GDM, in the Cook Islands. Methods We analysed two Te Marae Ora Cook Islands Ministry of Health datasets, the Non-Communicable Diseases (NCD) register examining demographic data for the period 1967 to December 2018 and same for the GDM register from January 2009 to December 2018. Results Of the 1270 diabetes cases, 53% were female and half were aged 45-64 years. There were 54 pre-diabetes cases and 146 GDM. Of the 20 GDM cases who developed type 2 diabetes, 80% were diagnosed before the age of 40 years. Data quality was poor. Discussion The Cook Islands diabetes registers provide important data to inform priorities for diabetes-related preventative and treatment measures. A data analyst has been employed to ensure quality, regularly audited data and information systems.