INTRODUCTION: Diabetes is a serious and increasing global health burden and estimates of prevalence are essential for appropriate allocation of resources and monitoring of trends. METHODS: We conducted a literature search of studies reporting the age-specific prevalence for diabetes and used the Analytic Hierarchy Process to systematically select studies to generate estimates for 219 countries and territories. Estimates for countries without available source data were modelled from pooled estimates of countries that were similar in regard to geography, ethnicity, and economic development. Logistic regression was applied to generate smoothed age-specific prevalence estimates for adults 20-79 years which were then applied to population estimates for 2013 and 2035. RESULTS: A total of 744 data sources were considered and 174 included, representing 130 countries. In 2013, 382 million people had diabetes; this number is expected to rise to 592 million by 2035. Most people with diabetes live in low- and middle-income countries and these will experience the greatest increase in cases of diabetes over the next 22 years. CONCLUSION: The new estimates of diabetes in adults confirm the large burden of diabetes, especially in developing countries. Estimates will be updated annually including the most recent, high-quality data available.