BACKGROUND: As the global prevalence of diabetes increases, so will the numbers of people with diabetic retinopathy. Our review aimed to provide a comprehensive picture of available studies of diabetic retinopathy and how prevalence varies around the developed and developing world. METHODS: A detailed literature search using PubMed was undertaken. The following search term was used: 'diabetic retinopathy AND prevalence'. The titles and abstracts of all publications identified by the search were reviewed and 492 studies were retrieved. Inclusion and exclusion criteria were applied. RESULTS: A total of 72 articles from 33 countries were included. There were only 26 population-based studies using fundus photography (12 in developing countries), of which only 16 (eight in developing countries) were published since 2000. Prevalence estimates varied from as low as 10% to as high as 61% in persons with known diabetes and from 1.5 to 31% in newly diagnosed diabetes. Across all the studies, the median (interquartile range) prevalence of any diabetic retinopathy in known diabetes was 27.9% (22-37%) and 10.5% (6-16%) in newly diagnosed diabetes. Prevalence of diabetic retinopathy was higher in developing countries. CONCLUSION: Significant gaps exist in that reliable population-based data from developing nations and indigenous populations in particular are lacking. Major differences in study characteristics and methodologies make comparisons very difficult. More research is required and study methodologies must be better standardized. This will provide important information for prevention and treatment strategies.