The fractal dimension (D(f)) of the retinal vasculature is a global measure of its branching pattern complexity. We examined the relationship of retinal D(f) with diabetes.We conducted a cross-sectional study of 1,577 participants with diabetes and impaired glucose metabolism and normal controls from the population-based Australian Diabetes, Obesity and Lifestyle (AusDiab) study. Retinal D(f) was quantified from fundus photographs using a computer-based programme and diabetes status was determined by oral glucose tolerance test based on the WHO criteria.After adjustment for age, sex and vascular risk factors, persons with higher retinal D(f) were more likely to have diabetes (OR 1.56; 95% CI 1.14-2.14, highest vs lowest fractal tertile). This relationship remained with further adjustment for retinal arteriolar calibre and presence of retinopathy (OR 1.64; 95% CI 1.19-2.27), and after excluding participants with retinopathy (OR 1.60; 95% CI 1.16-2.21). Retinal D (f) was not related to impaired glucose tolerance or impaired fasting glucose (OR 1.19; 95% CI 0.85-1.67).Individuals with diabetes, but not with impaired glucose metabolism, have greater retinal D(f), reflecting greater complexity of the retinal vasculature. Our findings suggest the presence of early microvascular changes in the retinal vasculature of persons with diabetes, even in the absence of overt retinopathy.